[PATCH v6 0/3] Enabling ATA Command Priorities

[PATCH v6 0/3] Enabling ATA Command Priorities

[Adam Manzanares]

This patch builds ATA commands with high priority if the iocontext of a process
is set to real time. The goal of the patch is to improve tail latencies of 
workloads that use higher queue depths. This requires setting the iocontext 
ioprio on the request when it is initialized

This patch has been tested with an Ultrastar HE8 HDD and cuts the 
the p99.99 tail latency of foreground IO from 2s down to 72ms when
using the deadline scheduler. This patch works independently of the
scheduler so it can be used with all of the currently available 
request based schedulers. 

Foreground IO, for the previously described results, is an async fio job 
submitting 4K read requests at a QD of 1 to the HDD. The foreground IO is set 
with the iopriority class of real time. The background workload is another fio
job submitting read requests at a QD of 32 to the same HDD with default 
iopriority.

This feature is enabled for ATA devices by setting the ata ncq_prio_on device 
attribute to 1. An ATA device is also checked to see if the device supports per
command priority.

v6:
 - Removed fusion mpt sas prio related code deletion
 - Renamed ata device attribute that enables priority cmds to the device

v5:
 - Updated block patch commit message to indicate the why and not the how
v4:
 - Added blk_rq_set_prio function to associate request prio with ioc prio
 - In init_request_from_bio use bio_prio if it is valid
 - Added ata enable_prio dev attribute to sysfs to enable prioritized commands

v3:
 - Removed null dereference issue in blk-core
 - Renamed queue sysfs entries for clarity
 - Added documentation for sysfs queue entry

v2:
 - Add queue flag to set iopriority going to the request
 - If queue flag set, send iopriority class to ata_build_rw_tf
 - Remove redundant code in ata_ncq_prio_enabled function.


Adam Manzanares (3):
  block: Add iocontext priority to request
  ata: Enabling ATA Command Priorities
  ata: ATA Command Priority Disabled By Default

 block/blk-core.c          |  4 ++-
 drivers/ata/libahci.c     |  1 +
 drivers/ata/libata-core.c | 35 +++++++++++++++++++++-
 drivers/ata/libata-scsi.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++-
 drivers/ata/libata.h      |  2 +-
 include/linux/ata.h       |  6 ++++
 include/linux/blkdev.h    | 14 +++++++++
 include/linux/libata.h    | 25 ++++++++++++++++
 8 files changed, 157 insertions(+), 4 deletions(-)

-- 
2.1.4

[PATCH v6 1/3] block: Add iocontext priority to request

[Adam Manzanares]

Patch adds an association between iocontext ioprio and the ioprio of a
request. This is done to enable request based drivers the ability to
act on priority information stored in the request. An example being
ATA devices that support command priorities. If the ATA driver discovers
that the device supports command priorities and the request has valid
priority information indicating the request is high priority, then a high
priority command can be sent to the device. This should improve tail
latencies for high priority IO on any device that queues requests
internally and can make use of the priority information stored in the
request.

The ioprio of the request is set in blk_rq_set_prio which takes the
request and the ioc as arguments. If the ioc is valid in blk_rq_set_prio
then the iopriority of the request is set as the iopriority of the ioc.
In init_request_from_bio a check is made to see if the ioprio of the bio
is valid and if so then the request prio comes from the bio.

Signed-off-by: Adam Manzananares <adam.manzanares@wdc.com>
---
 block/blk-core.c       |  4 +++-
 include/linux/blkdev.h | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 14d7c07..361b1b9 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1153,6 +1153,7 @@ static struct request *__get_request(struct request_list *rl, int op,
 
 	blk_rq_init(q, rq);
 	blk_rq_set_rl(rq, rl);
+	blk_rq_set_prio(rq, ioc);
 	req_set_op_attrs(rq, op, op_flags | REQ_ALLOCED);
 
 	/* init elvpriv */
@@ -1656,7 +1657,8 @@ void init_request_from_bio(struct request *req, struct bio *bio)
 
 	req->errors = 0;
 	req->__sector = bio->bi_iter.bi_sector;
-	req->ioprio = bio_prio(bio);
+	if (ioprio_valid(bio_prio(bio)))
+		req->ioprio = bio_prio(bio);
 	blk_rq_bio_prep(req->q, req, bio);
 }
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c47c358..9a0ceaa 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -934,6 +934,20 @@ static inline unsigned int blk_rq_count_bios(struct request *rq)
 }
 
 /*
+ * blk_rq_set_prio - associate a request with prio from ioc
+ * @rq: request of interest
+ * @ioc: target iocontext
+ *
+ * Assocate request prio with ioc prio so request based drivers
+ * can leverage priority information.
+ */
+static inline void blk_rq_set_prio(struct request *rq, struct io_context *ioc)
+{
+	if (ioc)
+		rq->ioprio = ioc->ioprio;
+}
+
+/*
  * Request issue related functions.
  */
 extern struct request *blk_peek_request(struct request_queue *q);
-- 
2.1.4

Re: [PATCH v6 1/3] block: Add iocontext priority to request

[Tejun Heo]

Hello,

On Mon, Oct 17, 2016 at 11:27:28AM -0700, Adam Manzanares wrote:
> Patch adds an association between iocontext ioprio and the ioprio of a
> request. This is done to enable request based drivers the ability to
> act on priority information stored in the request. An example being
> ATA devices that support command priorities. If the ATA driver discovers
> that the device supports command priorities and the request has valid
> priority information indicating the request is high priority, then a high
> priority command can be sent to the device. This should improve tail
> latencies for high priority IO on any device that queues requests
> internally and can make use of the priority information stored in the
> request.
> 
> The ioprio of the request is set in blk_rq_set_prio which takes the
> request and the ioc as arguments. If the ioc is valid in blk_rq_set_prio
> then the iopriority of the request is set as the iopriority of the ioc.
> In init_request_from_bio a check is made to see if the ioprio of the bio
> is valid and if so then the request prio comes from the bio.
> 
> Signed-off-by: Adam Manzananares <adam.manzanares@wdc.com>

Jens, if you're okay with it, I can route this through
libata/for-4.10, or this can be applied to block and libata tree can
pull from it.

Thanks.

-- 
tejun

Re: [PATCH v6 1/3] block: Add iocontext priority to request

[Jens Axboe]

On 10/19/2016 12:05 PM, Tejun Heo wrote:
> Hello,
>
> On Mon, Oct 17, 2016 at 11:27:28AM -0700, Adam Manzanares wrote:
>> Patch adds an association between iocontext ioprio and the ioprio of a
>> request. This is done to enable request based drivers the ability to
>> act on priority information stored in the request. An example being
>> ATA devices that support command priorities. If the ATA driver discovers
>> that the device supports command priorities and the request has valid
>> priority information indicating the request is high priority, then a high
>> priority command can be sent to the device. This should improve tail
>> latencies for high priority IO on any device that queues requests
>> internally and can make use of the priority information stored in the
>> request.
>>
>> The ioprio of the request is set in blk_rq_set_prio which takes the
>> request and the ioc as arguments. If the ioc is valid in blk_rq_set_prio
>> then the iopriority of the request is set as the iopriority of the ioc.
>> In init_request_from_bio a check is made to see if the ioprio of the bio
>> is valid and if so then the request prio comes from the bio.
>>
>> Signed-off-by: Adam Manzananares <adam.manzanares@wdc.com>
>
> Jens, if you're okay with it, I can route this through
> libata/for-4.10, or this can be applied to block and libata tree can
> pull from it.

I'm fine with that, add my Reviewed-by and funnel it through the libata
tree.

-- 
Jens Axboe

[PATCH v6 2/3] ata: Enabling ATA Command Priorities

[Adam Manzanares]

This patch checks to see if an ATA device supports NCQ command priorities.
If so and the user has specified an iocontext that indicates
IO_PRIO_CLASS_RT then we build a tf with a high priority command.

This is done to improve the tail latency of commands that are high
priority by passing priority to the device.

Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
---
 drivers/ata/libata-core.c | 35 ++++++++++++++++++++++++++++++++++-
 drivers/ata/libata-scsi.c |  6 +++++-
 drivers/ata/libata.h      |  2 +-
 include/linux/ata.h       |  6 ++++++
 include/linux/libata.h    | 18 ++++++++++++++++++
 5 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 223a770..181b530 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -739,6 +739,7 @@ u64 ata_tf_read_block(const struct ata_taskfile *tf, struct ata_device *dev)
  *	@n_block: Number of blocks
  *	@tf_flags: RW/FUA etc...
  *	@tag: tag
+ *	@class: IO priority class
  *
  *	LOCKING:
  *	None.
@@ -753,7 +754,7 @@ u64 ata_tf_read_block(const struct ata_taskfile *tf, struct ata_device *dev)
  */
 int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 		    u64 block, u32 n_block, unsigned int tf_flags,
-		    unsigned int tag)
+		    unsigned int tag, int class)
 {
 	tf->flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
 	tf->flags |= tf_flags;
@@ -785,6 +786,12 @@ int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 		tf->device = ATA_LBA;
 		if (tf->flags & ATA_TFLAG_FUA)
 			tf->device |= 1 << 7;
+
+		if (ata_ncq_prio_enabled(dev)) {
+			if (class == IOPRIO_CLASS_RT)
+				tf->hob_nsect |= ATA_PRIO_HIGH <<
+						 ATA_SHIFT_PRIO;
+		}
 	} else if (dev->flags & ATA_DFLAG_LBA) {
 		tf->flags |= ATA_TFLAG_LBA;
 
@@ -2156,6 +2163,30 @@ static void ata_dev_config_ncq_non_data(struct ata_device *dev)
 	}
 }
 
+static void ata_dev_config_ncq_prio(struct ata_device *dev)
+{
+	struct ata_port *ap = dev->link->ap;
+	unsigned int err_mask;
+
+	err_mask = ata_read_log_page(dev,
+				     ATA_LOG_SATA_ID_DEV_DATA,
+				     ATA_LOG_SATA_SETTINGS,
+				     ap->sector_buf,
+				     1);
+	if (err_mask) {
+		ata_dev_dbg(dev,
+			    "failed to get Identify Device data, Emask 0x%x\n",
+			    err_mask);
+		return;
+	}
+
+	if (ap->sector_buf[ATA_LOG_NCQ_PRIO_OFFSET] & BIT(3))
+		dev->flags |= ATA_DFLAG_NCQ_PRIO;
+	else
+		ata_dev_dbg(dev, "SATA page does not support priority\n");
+
+}
+
 static int ata_dev_config_ncq(struct ata_device *dev,
 			       char *desc, size_t desc_sz)
 {
@@ -2205,6 +2236,8 @@ static int ata_dev_config_ncq(struct ata_device *dev,
 			ata_dev_config_ncq_send_recv(dev);
 		if (ata_id_has_ncq_non_data(dev->id))
 			ata_dev_config_ncq_non_data(dev);
+		if (ata_id_has_ncq_prio(dev->id))
+			ata_dev_config_ncq_prio(dev);
 	}
 
 	return 0;
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 9cceb4a..2bccc3c 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -50,6 +50,7 @@
 #include <linux/uaccess.h>
 #include <linux/suspend.h>
 #include <asm/unaligned.h>
+#include <linux/ioprio.h>
 
 #include "libata.h"
 #include "libata-transport.h"
@@ -1755,6 +1756,8 @@ static unsigned int ata_scsi_rw_xlat(struct ata_queued_cmd *qc)
 {
 	struct scsi_cmnd *scmd = qc->scsicmd;
 	const u8 *cdb = scmd->cmnd;
+	struct request *rq = scmd->request;
+	int class = IOPRIO_PRIO_CLASS(req_get_ioprio(rq));
 	unsigned int tf_flags = 0;
 	u64 block;
 	u32 n_block;
@@ -1821,7 +1824,8 @@ static unsigned int ata_scsi_rw_xlat(struct ata_queued_cmd *qc)
 	qc->nbytes = n_block * scmd->device->sector_size;
 
 	rc = ata_build_rw_tf(&qc->tf, qc->dev, block, n_block, tf_flags,
-			     qc->tag);
+			     qc->tag, class);
+
 	if (likely(rc == 0))
 		return 0;
 
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index 3b301a4..8f3a559 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -66,7 +66,7 @@ extern u64 ata_tf_to_lba48(const struct ata_taskfile *tf);
 extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag);
 extern int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 			   u64 block, u32 n_block, unsigned int tf_flags,
-			   unsigned int tag);
+			   unsigned int tag, int class);
 extern u64 ata_tf_read_block(const struct ata_taskfile *tf,
 			     struct ata_device *dev);
 extern unsigned ata_exec_internal(struct ata_device *dev,
diff --git a/include/linux/ata.h b/include/linux/ata.h
index fdb1803..af6859b 100644
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -348,6 +348,7 @@ enum {
 	ATA_LOG_DEVSLP_DETO	  = 0x01,
 	ATA_LOG_DEVSLP_VALID	  = 0x07,
 	ATA_LOG_DEVSLP_VALID_MASK = 0x80,
+	ATA_LOG_NCQ_PRIO_OFFSET   = 0x09,
 
 	/* NCQ send and receive log */
 	ATA_LOG_NCQ_SEND_RECV_SUBCMDS_OFFSET	= 0x00,
@@ -940,6 +941,11 @@ static inline bool ata_id_has_ncq_non_data(const u16 *id)
 	return id[ATA_ID_SATA_CAPABILITY_2] & BIT(5);
 }
 
+static inline bool ata_id_has_ncq_prio(const u16 *id)
+{
+	return id[ATA_ID_SATA_CAPABILITY] & BIT(12);
+}
+
 static inline bool ata_id_has_trim(const u16 *id)
 {
 	if (ata_id_major_version(id) >= 7 &&
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 616eef4..1a524cf 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -166,6 +166,7 @@ enum {
 	ATA_DFLAG_NO_UNLOAD	= (1 << 17), /* device doesn't support unload */
 	ATA_DFLAG_UNLOCK_HPA	= (1 << 18), /* unlock HPA */
 	ATA_DFLAG_NCQ_SEND_RECV = (1 << 19), /* device supports NCQ SEND and RECV */
+	ATA_DFLAG_NCQ_PRIO	= (1 << 20), /* device supports NCQ priority */
 	ATA_DFLAG_INIT_MASK	= (1 << 24) - 1,
 
 	ATA_DFLAG_DETACH	= (1 << 24),
@@ -342,7 +343,9 @@ enum {
 	ATA_SHIFT_PIO		= 0,
 	ATA_SHIFT_MWDMA		= ATA_SHIFT_PIO + ATA_NR_PIO_MODES,
 	ATA_SHIFT_UDMA		= ATA_SHIFT_MWDMA + ATA_NR_MWDMA_MODES,
+	ATA_SHIFT_PRIO		= 6,
 
+	ATA_PRIO_HIGH		= 2,
 	/* size of buffer to pad xfers ending on unaligned boundaries */
 	ATA_DMA_PAD_SZ		= 4,
 
@@ -1610,6 +1613,21 @@ static inline int ata_ncq_enabled(struct ata_device *dev)
 			      ATA_DFLAG_NCQ)) == ATA_DFLAG_NCQ;
 }
 
+/**
+ *	ata_ncq_prio_enabled - Test whether NCQ prio is enabled
+ *	@dev: ATA device to test for
+ *
+ *	LOCKING:
+ *	spin_lock_irqsave(host lock)
+ *
+ *	RETURNS:
+ *	1 if NCQ prio is enabled for @dev, 0 otherwise.
+ */
+static inline int ata_ncq_prio_enabled(struct ata_device *dev)
+{
+	return (dev->flags & ATA_DFLAG_NCQ_PRIO) == ATA_DFLAG_NCQ_PRIO;
+}
+
 static inline bool ata_fpdma_dsm_supported(struct ata_device *dev)
 {
 	return (dev->flags & ATA_DFLAG_NCQ_SEND_RECV) &&
-- 
2.1.4

Re: [PATCH v6 2/3] ata: Enabling ATA Command Priorities

[Tejun Heo]

Hello,

I removed ata_ncq_prio_enabled() as it was colliding with the sysfs
file rename and these trivial test functions tend to obscure more than
help anything.

Thanks.

------ 8< ------
>From 8e061784b51ec4a4efed0deaafb5bd9725bf5b06 Mon Sep 17 00:00:00 2001
From: Adam Manzanares <adam.manzanares@hgst.com>
Date: Mon, 17 Oct 2016 11:27:29 -0700
Subject: [PATCH 1/2] ata: Enabling ATA Command Priorities

This patch checks to see if an ATA device supports NCQ command priorities.
If so and the user has specified an iocontext that indicates
IO_PRIO_CLASS_RT then we build a tf with a high priority command.

This is done to improve the tail latency of commands that are high
priority by passing priority to the device.

tj: Removed trivial ata_ncq_prio_enabled() and open-coded the test.

Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 drivers/ata/libata-core.c | 35 ++++++++++++++++++++++++++++++++++-
 drivers/ata/libata-scsi.c |  6 +++++-
 drivers/ata/libata.h      |  2 +-
 include/linux/ata.h       |  6 ++++++
 include/linux/libata.h    |  3 +++
 5 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 223a770..8346faf 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -739,6 +739,7 @@ u64 ata_tf_read_block(const struct ata_taskfile *tf, struct ata_device *dev)
  *	@n_block: Number of blocks
  *	@tf_flags: RW/FUA etc...
  *	@tag: tag
+ *	@class: IO priority class
  *
  *	LOCKING:
  *	None.
@@ -753,7 +754,7 @@ u64 ata_tf_read_block(const struct ata_taskfile *tf, struct ata_device *dev)
  */
 int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 		    u64 block, u32 n_block, unsigned int tf_flags,
-		    unsigned int tag)
+		    unsigned int tag, int class)
 {
 	tf->flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
 	tf->flags |= tf_flags;
@@ -785,6 +786,12 @@ int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 		tf->device = ATA_LBA;
 		if (tf->flags & ATA_TFLAG_FUA)
 			tf->device |= 1 << 7;
+
+		if (dev->flags & ATA_DFLAG_NCQ_PRIO) {
+			if (class == IOPRIO_CLASS_RT)
+				tf->hob_nsect |= ATA_PRIO_HIGH <<
+						 ATA_SHIFT_PRIO;
+		}
 	} else if (dev->flags & ATA_DFLAG_LBA) {
 		tf->flags |= ATA_TFLAG_LBA;
 
@@ -2156,6 +2163,30 @@ static void ata_dev_config_ncq_non_data(struct ata_device *dev)
 	}
 }
 
+static void ata_dev_config_ncq_prio(struct ata_device *dev)
+{
+	struct ata_port *ap = dev->link->ap;
+	unsigned int err_mask;
+
+	err_mask = ata_read_log_page(dev,
+				     ATA_LOG_SATA_ID_DEV_DATA,
+				     ATA_LOG_SATA_SETTINGS,
+				     ap->sector_buf,
+				     1);
+	if (err_mask) {
+		ata_dev_dbg(dev,
+			    "failed to get Identify Device data, Emask 0x%x\n",
+			    err_mask);
+		return;
+	}
+
+	if (ap->sector_buf[ATA_LOG_NCQ_PRIO_OFFSET] & BIT(3))
+		dev->flags |= ATA_DFLAG_NCQ_PRIO;
+	else
+		ata_dev_dbg(dev, "SATA page does not support priority\n");
+
+}
+
 static int ata_dev_config_ncq(struct ata_device *dev,
 			       char *desc, size_t desc_sz)
 {
@@ -2205,6 +2236,8 @@ static int ata_dev_config_ncq(struct ata_device *dev,
 			ata_dev_config_ncq_send_recv(dev);
 		if (ata_id_has_ncq_non_data(dev->id))
 			ata_dev_config_ncq_non_data(dev);
+		if (ata_id_has_ncq_prio(dev->id))
+			ata_dev_config_ncq_prio(dev);
 	}
 
 	return 0;
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 9cceb4a..2bccc3c 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -50,6 +50,7 @@
 #include <linux/uaccess.h>
 #include <linux/suspend.h>
 #include <asm/unaligned.h>
+#include <linux/ioprio.h>
 
 #include "libata.h"
 #include "libata-transport.h"
@@ -1755,6 +1756,8 @@ static unsigned int ata_scsi_rw_xlat(struct ata_queued_cmd *qc)
 {
 	struct scsi_cmnd *scmd = qc->scsicmd;
 	const u8 *cdb = scmd->cmnd;
+	struct request *rq = scmd->request;
+	int class = IOPRIO_PRIO_CLASS(req_get_ioprio(rq));
 	unsigned int tf_flags = 0;
 	u64 block;
 	u32 n_block;
@@ -1821,7 +1824,8 @@ static unsigned int ata_scsi_rw_xlat(struct ata_queued_cmd *qc)
 	qc->nbytes = n_block * scmd->device->sector_size;
 
 	rc = ata_build_rw_tf(&qc->tf, qc->dev, block, n_block, tf_flags,
-			     qc->tag);
+			     qc->tag, class);
+
 	if (likely(rc == 0))
 		return 0;
 
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index 3b301a4..8f3a559 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -66,7 +66,7 @@ extern u64 ata_tf_to_lba48(const struct ata_taskfile *tf);
 extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag);
 extern int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 			   u64 block, u32 n_block, unsigned int tf_flags,
-			   unsigned int tag);
+			   unsigned int tag, int class);
 extern u64 ata_tf_read_block(const struct ata_taskfile *tf,
 			     struct ata_device *dev);
 extern unsigned ata_exec_internal(struct ata_device *dev,
diff --git a/include/linux/ata.h b/include/linux/ata.h
index fdb1803..af6859b 100644
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -348,6 +348,7 @@ enum {
 	ATA_LOG_DEVSLP_DETO	  = 0x01,
 	ATA_LOG_DEVSLP_VALID	  = 0x07,
 	ATA_LOG_DEVSLP_VALID_MASK = 0x80,
+	ATA_LOG_NCQ_PRIO_OFFSET   = 0x09,
 
 	/* NCQ send and receive log */
 	ATA_LOG_NCQ_SEND_RECV_SUBCMDS_OFFSET	= 0x00,
@@ -940,6 +941,11 @@ static inline bool ata_id_has_ncq_non_data(const u16 *id)
 	return id[ATA_ID_SATA_CAPABILITY_2] & BIT(5);
 }
 
+static inline bool ata_id_has_ncq_prio(const u16 *id)
+{
+	return id[ATA_ID_SATA_CAPABILITY] & BIT(12);
+}
+
 static inline bool ata_id_has_trim(const u16 *id)
 {
 	if (ata_id_major_version(id) >= 7 &&
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 616eef4..90b69a6 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -166,6 +166,7 @@ enum {
 	ATA_DFLAG_NO_UNLOAD	= (1 << 17), /* device doesn't support unload */
 	ATA_DFLAG_UNLOCK_HPA	= (1 << 18), /* unlock HPA */
 	ATA_DFLAG_NCQ_SEND_RECV = (1 << 19), /* device supports NCQ SEND and RECV */
+	ATA_DFLAG_NCQ_PRIO	= (1 << 20), /* device supports NCQ priority */
 	ATA_DFLAG_INIT_MASK	= (1 << 24) - 1,
 
 	ATA_DFLAG_DETACH	= (1 << 24),
@@ -342,7 +343,9 @@ enum {
 	ATA_SHIFT_PIO		= 0,
 	ATA_SHIFT_MWDMA		= ATA_SHIFT_PIO + ATA_NR_PIO_MODES,
 	ATA_SHIFT_UDMA		= ATA_SHIFT_MWDMA + ATA_NR_MWDMA_MODES,
+	ATA_SHIFT_PRIO		= 6,
 
+	ATA_PRIO_HIGH		= 2,
 	/* size of buffer to pad xfers ending on unaligned boundaries */
 	ATA_DMA_PAD_SZ		= 4,
 
-- 
2.7.4

[PATCH v6 3/3] ata: ATA Command Priority Disabled By Default

[Adam Manzanares]

Add a sysfs entry to turn on priority information being passed
to a ATA device. By default this feature is turned off.

This patch depends on ata: Enabling ATA Command Priorities

Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
---
 drivers/ata/libahci.c     |  1 +
 drivers/ata/libata-core.c |  2 +-
 drivers/ata/libata-scsi.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/libata.h    |  7 +++++
 4 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 0d028ea..0e17285 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -140,6 +140,7 @@ EXPORT_SYMBOL_GPL(ahci_shost_attrs);
 struct device_attribute *ahci_sdev_attrs[] = {
 	&dev_attr_sw_activity,
 	&dev_attr_unload_heads,
+	&dev_attr_ncq_prio_on,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ahci_sdev_attrs);
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 181b530..d8e1278 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -787,7 +787,7 @@ int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 		if (tf->flags & ATA_TFLAG_FUA)
 			tf->device |= 1 << 7;
 
-		if (ata_ncq_prio_enabled(dev)) {
+		if (ata_ncq_prio_enabled(dev) && ata_ncq_prio_on(dev)) {
 			if (class == IOPRIO_CLASS_RT)
 				tf->hob_nsect |= ATA_PRIO_HIGH <<
 						 ATA_SHIFT_PRIO;
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 2bccc3c..f2709ac 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -271,6 +271,73 @@ DEVICE_ATTR(unload_heads, S_IRUGO | S_IWUSR,
 	    ata_scsi_park_show, ata_scsi_park_store);
 EXPORT_SYMBOL_GPL(dev_attr_unload_heads);
 
+static ssize_t ata_ncq_prio_on_show(struct device *device,
+				    struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(device);
+	struct ata_port *ap;
+	struct ata_device *dev;
+	int rc = 0;
+	int ncq_prio_on;
+
+	ap = ata_shost_to_port(sdev->host);
+
+	spin_lock_irq(ap->lock);
+	dev = ata_scsi_find_dev(ap, sdev);
+	if (!dev) {
+		rc = -ENODEV;
+		goto unlock;
+	}
+
+	ncq_prio_on = ata_ncq_prio_on(dev);
+
+unlock:
+	spin_unlock_irq(ap->lock);
+
+	return rc ? rc : snprintf(buf, 20, "%u\n", ncq_prio_on);
+}
+
+static ssize_t ata_ncq_prio_on_store(struct device *device,
+				     struct device_attribute *attr,
+				     const char *buf, size_t len)
+{
+	struct scsi_device *sdev = to_scsi_device(device);
+	struct ata_port *ap;
+	struct ata_device *dev;
+	long int input;
+	unsigned long flags;
+	int rc;
+
+	rc = kstrtol(buf, 10, &input);
+	if (rc)
+		return rc;
+	if ((input < 0) || (input > 1))
+		return -EINVAL;
+
+	ap = ata_shost_to_port(sdev->host);
+
+	spin_lock_irqsave(ap->lock, flags);
+	dev = ata_scsi_find_dev(ap, sdev);
+	if (unlikely(!dev)) {
+		rc = -ENODEV;
+		goto unlock;
+	}
+
+	if (input)
+		dev->flags |= ATA_DFLAG_NCQ_PRIO_ON;
+	else
+		dev->flags &= ~ATA_DFLAG_NCQ_PRIO_ON;
+
+unlock:
+	spin_unlock_irqrestore(ap->lock, flags);
+
+	return rc ? rc : len;
+}
+
+DEVICE_ATTR(ncq_prio_on, S_IRUGO | S_IWUSR,
+	    ata_ncq_prio_on_show, ata_ncq_prio_on_store);
+EXPORT_SYMBOL_GPL(dev_attr_ncq_prio_on);
+
 void ata_scsi_set_sense(struct ata_device *dev, struct scsi_cmnd *cmd,
 			u8 sk, u8 asc, u8 ascq)
 {
@@ -402,6 +469,7 @@ EXPORT_SYMBOL_GPL(dev_attr_sw_activity);
 
 struct device_attribute *ata_common_sdev_attrs[] = {
 	&dev_attr_unload_heads,
+	&dev_attr_ncq_prio_on,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ata_common_sdev_attrs);
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 1a524cf..5f24ca1 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -167,6 +167,7 @@ enum {
 	ATA_DFLAG_UNLOCK_HPA	= (1 << 18), /* unlock HPA */
 	ATA_DFLAG_NCQ_SEND_RECV = (1 << 19), /* device supports NCQ SEND and RECV */
 	ATA_DFLAG_NCQ_PRIO	= (1 << 20), /* device supports NCQ priority */
+	ATA_DFLAG_NCQ_PRIO_ON	= (1 << 21), /* Priority cmds sent to dev */
 	ATA_DFLAG_INIT_MASK	= (1 << 24) - 1,
 
 	ATA_DFLAG_DETACH	= (1 << 24),
@@ -545,6 +546,7 @@ typedef void (*ata_postreset_fn_t)(struct ata_link *link, unsigned int *classes)
 
 extern struct device_attribute dev_attr_link_power_management_policy;
 extern struct device_attribute dev_attr_unload_heads;
+extern struct device_attribute dev_attr_ncq_prio_on;
 extern struct device_attribute dev_attr_em_message_type;
 extern struct device_attribute dev_attr_em_message;
 extern struct device_attribute dev_attr_sw_activity;
@@ -1628,6 +1630,11 @@ static inline int ata_ncq_prio_enabled(struct ata_device *dev)
 	return (dev->flags & ATA_DFLAG_NCQ_PRIO) == ATA_DFLAG_NCQ_PRIO;
 }
 
+static inline int ata_ncq_prio_on(struct ata_device *dev)
+{
+	return ((dev->flags & ATA_DFLAG_NCQ_PRIO_ON) == ATA_DFLAG_NCQ_PRIO_ON);
+}
+
 static inline bool ata_fpdma_dsm_supported(struct ata_device *dev)
 {
 	return (dev->flags & ATA_DFLAG_NCQ_SEND_RECV) &&
-- 
2.1.4

Re: [PATCH v6 3/3] ata: ATA Command Priority Disabled By Default

[Tejun Heo]

On Mon, Oct 17, 2016 at 11:27:30AM -0700, Adam Manzanares wrote:
> Add a sysfs entry to turn on priority information being passed
> to a ATA device. By default this feature is turned off.
> 
> This patch depends on ata: Enabling ATA Command Priorities
> 
> Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
> ---
>  drivers/ata/libahci.c     |  1 +
>  drivers/ata/libata-core.c |  2 +-
>  drivers/ata/libata-scsi.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/libata.h    |  7 +++++
>  4 files changed, 77 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
> index 0d028ea..0e17285 100644
> --- a/drivers/ata/libahci.c
> +++ b/drivers/ata/libahci.c
> @@ -140,6 +140,7 @@ EXPORT_SYMBOL_GPL(ahci_shost_attrs);
>  struct device_attribute *ahci_sdev_attrs[] = {
>  	&dev_attr_sw_activity,
>  	&dev_attr_unload_heads,
> +	&dev_attr_ncq_prio_on,

I'll rename it to ncq_prio_enable while applying but otherwise looks
good to me.

Thanks.

-- 
tejun

Re: [PATCH v6 3/3] ata: ATA Command Priority Disabled By Default

[Adam Manzanares]

The 10/19/2016 14:05, Tejun Heo wrote:
> On Mon, Oct 17, 2016 at 11:27:30AM -0700, Adam Manzanares wrote:
> > Add a sysfs entry to turn on priority information being passed
> > to a ATA device. By default this feature is turned off.
> > 
> > This patch depends on ata: Enabling ATA Command Priorities
> > 
> > Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
> > ---
> >  drivers/ata/libahci.c     |  1 +
> >  drivers/ata/libata-core.c |  2 +-
> >  drivers/ata/libata-scsi.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/libata.h    |  7 +++++
> >  4 files changed, 77 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
> > index 0d028ea..0e17285 100644
> > --- a/drivers/ata/libahci.c
> > +++ b/drivers/ata/libahci.c
> > @@ -140,6 +140,7 @@ EXPORT_SYMBOL_GPL(ahci_shost_attrs);
> >  struct device_attribute *ahci_sdev_attrs[] = {
> >  	&dev_attr_sw_activity,
> >  	&dev_attr_unload_heads,
> > +	&dev_attr_ncq_prio_on,
> 
> I'll rename it to ncq_prio_enable while applying but otherwise looks
> good to me.

Sounds good.

Take care,
Adam

> 
> Thanks.
> 
> -- 
> tejun

Re: [PATCH v6 3/3] ata: ATA Command Priority Disabled By Default

[Tejun Heo]

Hello,

Removed ata_ncq_prio_on() and renamed _on to _enable.  If I messed up
anything, please let me know.

Also, can you please send a follow-up patch to make the store function
reject prio enabling if the device doesn't support it?

Thanks.

------ 8< ------
>From 84f95243b5439a20c33837075b88926bfa00c4ec Mon Sep 17 00:00:00 2001
From: Adam Manzanares <adam.manzanares@hgst.com>
Date: Mon, 17 Oct 2016 11:27:30 -0700
Subject: [PATCH 2/2] ata: ATA Command Priority Disabled By Default

Add a sysfs entry to turn on priority information being passed
to a ATA device. By default this feature is turned off.

This patch depends on ata: Enabling ATA Command Priorities

tj: Renamed ncq_prio_on to ncq_prio_enable and removed trivial
    ata_ncq_prio_on() and open-coded the test.

Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 drivers/ata/libahci.c     |  1 +
 drivers/ata/libata-core.c |  3 ++-
 drivers/ata/libata-scsi.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/libata.h    |  2 ++
 4 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 0d028ea..ee7db31 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -140,6 +140,7 @@ EXPORT_SYMBOL_GPL(ahci_shost_attrs);
 struct device_attribute *ahci_sdev_attrs[] = {
 	&dev_attr_sw_activity,
 	&dev_attr_unload_heads,
+	&dev_attr_ncq_prio_enable,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ahci_sdev_attrs);
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 8346faf..b294339 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -787,7 +787,8 @@ int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
 		if (tf->flags & ATA_TFLAG_FUA)
 			tf->device |= 1 << 7;
 
-		if (dev->flags & ATA_DFLAG_NCQ_PRIO) {
+		if ((dev->flags & ATA_DFLAG_NCQ_PRIO) &&
+		    (dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLE)) {
 			if (class == IOPRIO_CLASS_RT)
 				tf->hob_nsect |= ATA_PRIO_HIGH <<
 						 ATA_SHIFT_PRIO;
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 2bccc3c..87597a3 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -271,6 +271,73 @@ DEVICE_ATTR(unload_heads, S_IRUGO | S_IWUSR,
 	    ata_scsi_park_show, ata_scsi_park_store);
 EXPORT_SYMBOL_GPL(dev_attr_unload_heads);
 
+static ssize_t ata_ncq_prio_enable_show(struct device *device,
+					struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(device);
+	struct ata_port *ap;
+	struct ata_device *dev;
+	bool ncq_prio_enable;
+	int rc = 0;
+
+	ap = ata_shost_to_port(sdev->host);
+
+	spin_lock_irq(ap->lock);
+	dev = ata_scsi_find_dev(ap, sdev);
+	if (!dev) {
+		rc = -ENODEV;
+		goto unlock;
+	}
+
+	ncq_prio_enable = dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLE;
+
+unlock:
+	spin_unlock_irq(ap->lock);
+
+	return rc ? rc : snprintf(buf, 20, "%u\n", ncq_prio_enable);
+}
+
+static ssize_t ata_ncq_prio_enable_store(struct device *device,
+					 struct device_attribute *attr,
+					 const char *buf, size_t len)
+{
+	struct scsi_device *sdev = to_scsi_device(device);
+	struct ata_port *ap;
+	struct ata_device *dev;
+	long int input;
+	unsigned long flags;
+	int rc;
+
+	rc = kstrtol(buf, 10, &input);
+	if (rc)
+		return rc;
+	if ((input < 0) || (input > 1))
+		return -EINVAL;
+
+	ap = ata_shost_to_port(sdev->host);
+
+	spin_lock_irqsave(ap->lock, flags);
+	dev = ata_scsi_find_dev(ap, sdev);
+	if (unlikely(!dev)) {
+		rc = -ENODEV;
+		goto unlock;
+	}
+
+	if (input)
+		dev->flags |= ATA_DFLAG_NCQ_PRIO_ENABLE;
+	else
+		dev->flags &= ~ATA_DFLAG_NCQ_PRIO_ENABLE;
+
+unlock:
+	spin_unlock_irqrestore(ap->lock, flags);
+
+	return rc ? rc : len;
+}
+
+DEVICE_ATTR(ncq_prio_enable, S_IRUGO | S_IWUSR,
+	    ata_ncq_prio_enable_show, ata_ncq_prio_enable_store);
+EXPORT_SYMBOL_GPL(dev_attr_ncq_prio_enable);
+
 void ata_scsi_set_sense(struct ata_device *dev, struct scsi_cmnd *cmd,
 			u8 sk, u8 asc, u8 ascq)
 {
@@ -402,6 +469,7 @@ EXPORT_SYMBOL_GPL(dev_attr_sw_activity);
 
 struct device_attribute *ata_common_sdev_attrs[] = {
 	&dev_attr_unload_heads,
+	&dev_attr_ncq_prio_enable,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ata_common_sdev_attrs);
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 90b69a6..c170be5 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -167,6 +167,7 @@ enum {
 	ATA_DFLAG_UNLOCK_HPA	= (1 << 18), /* unlock HPA */
 	ATA_DFLAG_NCQ_SEND_RECV = (1 << 19), /* device supports NCQ SEND and RECV */
 	ATA_DFLAG_NCQ_PRIO	= (1 << 20), /* device supports NCQ priority */
+	ATA_DFLAG_NCQ_PRIO_ENABLE = (1 << 21), /* Priority cmds sent to dev */
 	ATA_DFLAG_INIT_MASK	= (1 << 24) - 1,
 
 	ATA_DFLAG_DETACH	= (1 << 24),
@@ -545,6 +546,7 @@ typedef void (*ata_postreset_fn_t)(struct ata_link *link, unsigned int *classes)
 
 extern struct device_attribute dev_attr_link_power_management_policy;
 extern struct device_attribute dev_attr_unload_heads;
+extern struct device_attribute dev_attr_ncq_prio_enable;
 extern struct device_attribute dev_attr_em_message_type;
 extern struct device_attribute dev_attr_em_message;
 extern struct device_attribute dev_attr_sw_activity;
-- 
2.7.4

Re: [PATCH v6 3/3] ata: ATA Command Priority Disabled By Default

[Adam Manzanares]

The 10/19/2016 14:38, Tejun Heo wrote:
> Hello,
> 
> Removed ata_ncq_prio_on() and renamed _on to _enable.  If I messed up
> anything, please let me know.
> 

Works as expected. Thanks for cleaning this up.

> Also, can you please send a follow-up patch to make the store function
> reject prio enabling if the device doesn't support it?
> 

I'll send something out shortly.

Take care,
Adam

> Thanks.
> 
> ------ 8< ------
> From 84f95243b5439a20c33837075b88926bfa00c4ec Mon Sep 17 00:00:00 2001
> From: Adam Manzanares <adam.manzanares@hgst.com>
> Date: Mon, 17 Oct 2016 11:27:30 -0700
> Subject: [PATCH 2/2] ata: ATA Command Priority Disabled By Default
> 
> Add a sysfs entry to turn on priority information being passed
> to a ATA device. By default this feature is turned off.
> 
> This patch depends on ata: Enabling ATA Command Priorities
> 
> tj: Renamed ncq_prio_on to ncq_prio_enable and removed trivial
>     ata_ncq_prio_on() and open-coded the test.
> 
> Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> ---
>  drivers/ata/libahci.c     |  1 +
>  drivers/ata/libata-core.c |  3 ++-
>  drivers/ata/libata-scsi.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/libata.h    |  2 ++
>  4 files changed, 73 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
> index 0d028ea..ee7db31 100644
> --- a/drivers/ata/libahci.c
> +++ b/drivers/ata/libahci.c
> @@ -140,6 +140,7 @@ EXPORT_SYMBOL_GPL(ahci_shost_attrs);
>  struct device_attribute *ahci_sdev_attrs[] = {
>  	&dev_attr_sw_activity,
>  	&dev_attr_unload_heads,
> +	&dev_attr_ncq_prio_enable,
>  	NULL
>  };
>  EXPORT_SYMBOL_GPL(ahci_sdev_attrs);
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index 8346faf..b294339 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -787,7 +787,8 @@ int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
>  		if (tf->flags & ATA_TFLAG_FUA)
>  			tf->device |= 1 << 7;
>  
> -		if (dev->flags & ATA_DFLAG_NCQ_PRIO) {
> +		if ((dev->flags & ATA_DFLAG_NCQ_PRIO) &&
> +		    (dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLE)) {
>  			if (class == IOPRIO_CLASS_RT)
>  				tf->hob_nsect |= ATA_PRIO_HIGH <<
>  						 ATA_SHIFT_PRIO;
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 2bccc3c..87597a3 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -271,6 +271,73 @@ DEVICE_ATTR(unload_heads, S_IRUGO | S_IWUSR,
>  	    ata_scsi_park_show, ata_scsi_park_store);
>  EXPORT_SYMBOL_GPL(dev_attr_unload_heads);
>  
> +static ssize_t ata_ncq_prio_enable_show(struct device *device,
> +					struct device_attribute *attr, char *buf)
> +{
> +	struct scsi_device *sdev = to_scsi_device(device);
> +	struct ata_port *ap;
> +	struct ata_device *dev;
> +	bool ncq_prio_enable;
> +	int rc = 0;
> +
> +	ap = ata_shost_to_port(sdev->host);
> +
> +	spin_lock_irq(ap->lock);
> +	dev = ata_scsi_find_dev(ap, sdev);
> +	if (!dev) {
> +		rc = -ENODEV;
> +		goto unlock;
> +	}
> +
> +	ncq_prio_enable = dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLE;
> +
> +unlock:
> +	spin_unlock_irq(ap->lock);
> +
> +	return rc ? rc : snprintf(buf, 20, "%u\n", ncq_prio_enable);
> +}
> +
> +static ssize_t ata_ncq_prio_enable_store(struct device *device,
> +					 struct device_attribute *attr,
> +					 const char *buf, size_t len)
> +{
> +	struct scsi_device *sdev = to_scsi_device(device);
> +	struct ata_port *ap;
> +	struct ata_device *dev;
> +	long int input;
> +	unsigned long flags;
> +	int rc;
> +
> +	rc = kstrtol(buf, 10, &input);
> +	if (rc)
> +		return rc;
> +	if ((input < 0) || (input > 1))
> +		return -EINVAL;
> +
> +	ap = ata_shost_to_port(sdev->host);
> +
> +	spin_lock_irqsave(ap->lock, flags);
> +	dev = ata_scsi_find_dev(ap, sdev);
> +	if (unlikely(!dev)) {
> +		rc = -ENODEV;
> +		goto unlock;
> +	}
> +
> +	if (input)
> +		dev->flags |= ATA_DFLAG_NCQ_PRIO_ENABLE;
> +	else
> +		dev->flags &= ~ATA_DFLAG_NCQ_PRIO_ENABLE;
> +
> +unlock:
> +	spin_unlock_irqrestore(ap->lock, flags);
> +
> +	return rc ? rc : len;
> +}
> +
> +DEVICE_ATTR(ncq_prio_enable, S_IRUGO | S_IWUSR,
> +	    ata_ncq_prio_enable_show, ata_ncq_prio_enable_store);
> +EXPORT_SYMBOL_GPL(dev_attr_ncq_prio_enable);
> +
>  void ata_scsi_set_sense(struct ata_device *dev, struct scsi_cmnd *cmd,
>  			u8 sk, u8 asc, u8 ascq)
>  {
> @@ -402,6 +469,7 @@ EXPORT_SYMBOL_GPL(dev_attr_sw_activity);
>  
>  struct device_attribute *ata_common_sdev_attrs[] = {
>  	&dev_attr_unload_heads,
> +	&dev_attr_ncq_prio_enable,
>  	NULL
>  };
>  EXPORT_SYMBOL_GPL(ata_common_sdev_attrs);
> diff --git a/include/linux/libata.h b/include/linux/libata.h
> index 90b69a6..c170be5 100644
> --- a/include/linux/libata.h
> +++ b/include/linux/libata.h
> @@ -167,6 +167,7 @@ enum {
>  	ATA_DFLAG_UNLOCK_HPA	= (1 << 18), /* unlock HPA */
>  	ATA_DFLAG_NCQ_SEND_RECV = (1 << 19), /* device supports NCQ SEND and RECV */
>  	ATA_DFLAG_NCQ_PRIO	= (1 << 20), /* device supports NCQ priority */
> +	ATA_DFLAG_NCQ_PRIO_ENABLE = (1 << 21), /* Priority cmds sent to dev */
>  	ATA_DFLAG_INIT_MASK	= (1 << 24) - 1,
>  
>  	ATA_DFLAG_DETACH	= (1 << 24),
> @@ -545,6 +546,7 @@ typedef void (*ata_postreset_fn_t)(struct ata_link *link, unsigned int *classes)
>  
>  extern struct device_attribute dev_attr_link_power_management_policy;
>  extern struct device_attribute dev_attr_unload_heads;
> +extern struct device_attribute dev_attr_ncq_prio_enable;
>  extern struct device_attribute dev_attr_em_message_type;
>  extern struct device_attribute dev_attr_em_message;
>  extern struct device_attribute dev_attr_sw_activity;
> -- 
> 2.7.4
> 

Re: [PATCH v6 0/3] Enabling ATA Command Priorities

[Tejun Heo]

On Mon, Oct 17, 2016 at 11:27:27AM -0700, Adam Manzanares wrote:
> This patch builds ATA commands with high priority if the iocontext of a process
> is set to real time. The goal of the patch is to improve tail latencies of 
> workloads that use higher queue depths. This requires setting the iocontext 
> ioprio on the request when it is initialized
> 
> This patch has been tested with an Ultrastar HE8 HDD and cuts the 
> the p99.99 tail latency of foreground IO from 2s down to 72ms when
> using the deadline scheduler. This patch works independently of the
> scheduler so it can be used with all of the currently available 
> request based schedulers. 
> 
> Foreground IO, for the previously described results, is an async fio job 
> submitting 4K read requests at a QD of 1 to the HDD. The foreground IO is set 
> with the iopriority class of real time. The background workload is another fio
> job submitting read requests at a QD of 32 to the same HDD with default 
> iopriority.
> 
> This feature is enabled for ATA devices by setting the ata ncq_prio_on device 
> attribute to 1. An ATA device is also checked to see if the device supports per
> command priority.

Applied 1-3 to libata/for-4.10 w/ some modifications.

Thanks.

-- 
tejun