[PATCH] AHCI prefetch

[PATCH] AHCI prefetch

[Jeff Garzik]

This patch has been sitting in my tmp directory for ages.

We should probably turn this on, though the practical difference is
probably minimal.


diff --git a/drivers/scsi/ahci.c b/drivers/scsi/ahci.c
index 4e96ec5..973a794 100644
--- a/drivers/scsi/ahci.c
+++ b/drivers/scsi/ahci.c
@@ -64,8 +64,10 @@ enum {
 	AHCI_PORT_PRIV_DMA_SZ	= AHCI_CMD_SLOT_SZ + AHCI_CMD_TBL_SZ +
 				  AHCI_RX_FIS_SZ,
 	AHCI_IRQ_ON_SG		= (1 << 31),
+
 	AHCI_CMD_ATAPI		= (1 << 5),
 	AHCI_CMD_WRITE		= (1 << 6),
+	AHCI_CMD_PREFETCH	= (1 << 7),
 
 	RX_FIS_D2H_REG		= 0x40,	/* offset of D2H Register FIS data */
 
@@ -533,7 +535,7 @@ static void ahci_qc_prep(struct ata_queu
 	if (qc->tf.flags & ATA_TFLAG_WRITE)
 		opts |= AHCI_CMD_WRITE;
 	if (is_atapi_taskfile(&qc->tf))
-		opts |= AHCI_CMD_ATAPI;
+		opts |= AHCI_CMD_ATAPI | AHCI_CMD_PREFETCH;
 
 	pp->cmd_slot[0].opts = cpu_to_le32(opts);
 	pp->cmd_slot[0].status = 0;

Re: [PATCH] AHCI prefetch

[Tejun Heo]

On Sat, Mar 04, 2006 at 12:35:05PM -0500, Jeff Garzik wrote:
> 
> This patch has been sitting in my tmp directory for ages.
> 
> We should probably turn this on, though the practical difference is
> probably minimal.
> 

The patch works okay on my machine (ICH7R) although the patch didn't
apply to #upstream.  I'm not very sure about this change though.

1. Why apply it only to ATAPI devices?  ATA devices can benefit to.
   If it's because this bit shouldn't be turned on for NCQ, we can
   turn it on conditionally.  We'll probably need similar condition
   for ATAPI devices too if we support FIS-based PM switching.

2. I'm a bit skeptical whether this change will bring any noticeable
   performance improvement.  OTOH, this seems to be a good source for
   obscure problems on some controllers which might not implement/test
   this feature properly.  As more controllers implement AHCI spec,
   the possibility grows.

Anyways, here's the patch regenerated against #upstream.

diff --git a/drivers/scsi/ahci.c b/drivers/scsi/ahci.c
index 1c2ab3d..cfa6eaf 100644
--- a/drivers/scsi/ahci.c
+++ b/drivers/scsi/ahci.c
@@ -66,6 +66,7 @@ enum {
 	AHCI_IRQ_ON_SG		= (1 << 31),
 	AHCI_CMD_ATAPI		= (1 << 5),
 	AHCI_CMD_WRITE		= (1 << 6),
+	AHCI_CMD_PREFETCH	= (1 << 7),
 	AHCI_CMD_RESET		= (1 << 8),
 	AHCI_CMD_CLR_BUSY	= (1 << 10),
 
@@ -631,7 +632,7 @@ static void ahci_qc_prep(struct ata_queu
 	if (qc->tf.flags & ATA_TFLAG_WRITE)
 		opts |= AHCI_CMD_WRITE;
 	if (is_atapi)
-		opts |= AHCI_CMD_ATAPI;
+		opts |= AHCI_CMD_ATAPI | AHCI_CMD_PREFETCH;
 
 	ahci_fill_cmd_slot(pp, opts);
 }

Re: [PATCH] AHCI prefetch

[Jeff Garzik]

Tejun Heo wrote:
> On Sat, Mar 04, 2006 at 12:35:05PM -0500, Jeff Garzik wrote:
> 
>>This patch has been sitting in my tmp directory for ages.
>>
>>We should probably turn this on, though the practical difference is
>>probably minimal.
>>
> 
> 
> The patch works okay on my machine (ICH7R) although the patch didn't
> apply to #upstream.  I'm not very sure about this change though.
> 
> 1. Why apply it only to ATAPI devices?  ATA devices can benefit to.
>    If it's because this bit shouldn't be turned on for NCQ, we can
>    turn it on conditionally.  We'll probably need similar condition
>    for ATAPI devices too if we support FIS-based PM switching.

Main reason is that it will largely only have benefits on ATAPI devices, 
and I've only tested it on ATAPI devices.


> 2. I'm a bit skeptical whether this change will bring any noticeable
>    performance improvement.  OTOH, this seems to be a good source for

Agreed.


>    obscure problems on some controllers which might not implement/test
>    this feature properly.  As more controllers implement AHCI spec,
>    the possibility grows.

Agreed.


> Anyways, here's the patch regenerated against #upstream.

Could I trouble you for a resend, with a proper signed-off-by and patch 
description?

	Jeff

[PATCH] ahci: enable prefetching for PACKET commands

[Tejun Heo]

Turn on AHCI_CMD_PREFETCH for PACKET commands.  This hints the
controller that it can prefetch the CDB and the PRD entries.  This
patch is originally from Jeff Garzik.

Signed-off-by: Tejun Heo <htejun@gmail.com>

---

Jeff, I'll send two flavors of this patch.  The other one will enable
AHCI_CMD_PREFETCH for both ATA and ATAPI devices.  I've tested both
cases on ICH7R.

 ahci.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/ahci.c b/drivers/scsi/ahci.c
index 00dfdef..e97ab3e 100644
--- a/drivers/scsi/ahci.c
+++ b/drivers/scsi/ahci.c
@@ -66,6 +66,7 @@ enum {
 	AHCI_IRQ_ON_SG		= (1 << 31),
 	AHCI_CMD_ATAPI		= (1 << 5),
 	AHCI_CMD_WRITE		= (1 << 6),
+	AHCI_CMD_PREFETCH	= (1 << 7),
 	AHCI_CMD_RESET		= (1 << 8),
 	AHCI_CMD_CLR_BUSY	= (1 << 10),
 
@@ -631,7 +632,7 @@ static void ahci_qc_prep(struct ata_queu
 	if (qc->tf.flags & ATA_TFLAG_WRITE)
 		opts |= AHCI_CMD_WRITE;
 	if (is_atapi)
-		opts |= AHCI_CMD_ATAPI;
+		opts |= AHCI_CMD_ATAPI | AHCI_CMD_PREFETCH;
 
 	ahci_fill_cmd_slot(pp, opts);
 }

[PATCH] ahci: enable prefetching

[Tejun Heo]

Enable prefetching.  This hints AHCI controller that it can prefetch
PRT entries and CDB (for PACKET commands).  This is a hint.  AHCI
controller is free to ignore it or prefetch regardless of this bit.

Note that prefetching bit should be turned off for NCQ commands or
FIS-based switching PM support.

Signed-off-by: Tejun Heo <htejun@gmail.com>

---

And this is the second version.

 ahci.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/ahci.c b/drivers/scsi/ahci.c
index 00dfdef..454a393 100644
--- a/drivers/scsi/ahci.c
+++ b/drivers/scsi/ahci.c
@@ -66,6 +66,7 @@ enum {
 	AHCI_IRQ_ON_SG		= (1 << 31),
 	AHCI_CMD_ATAPI		= (1 << 5),
 	AHCI_CMD_WRITE		= (1 << 6),
+	AHCI_CMD_PREFETCH	= (1 << 7),
 	AHCI_CMD_RESET		= (1 << 8),
 	AHCI_CMD_CLR_BUSY	= (1 << 10),
 
@@ -627,7 +628,7 @@ static void ahci_qc_prep(struct ata_queu
 	/*
 	 * Fill in command slot information.
 	 */
-	opts = cmd_fis_len | n_elem << 16;
+	opts = AHCI_CMD_PREFETCH | cmd_fis_len | n_elem << 16;
 	if (qc->tf.flags & ATA_TFLAG_WRITE)
 		opts |= AHCI_CMD_WRITE;
 	if (is_atapi)