[PATCH v3 18/18] Documentation: sysfs-block-device: document command duration limits

Niklas Cassel
2023-01-24T19:05:47Z

From: Damien Le Moal <damien.lemoal@opensource.wdc.com>

Document ABI/testing/sysfs-block-device the sysfs attributes present
under /sys/block/*/device/duration_limits for ATA and SCSI devices
supporting the command duration limits feature.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
---
Documentation/ABI/testing/sysfs-block-device | 150 +++++++++++++++++++
1 file changed, 150 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-block-device b/Documentation/ABI/testing/sysfs-block-device
index 7ac7b19b2f72..3a32c86942f5 100644
--- a/Documentation/ABI/testing/sysfs-block-device
+++ b/Documentation/ABI/testing/sysfs-block-device
@@ -95,3 +95,153 @@ Description:
This file does not exist if the HBA driver does not implement
support for the SATA NCQ priority feature, regardless of the
device support for this feature.
+
+
+What: /sys/block/*/device/duration_limits/enable
+Date: Dec, 2022
+KernelVersion: v6.3
+Contact: linux-scsi@vger.kernel.org
+Description:
+ (RW) For ATA and SCSI devices supporting the command duration
+ limits feature, write to the file to turn on or off the
+ feature. By default this feature is turned off. If the device
+ does not support the command duration limits feature, this
+ attribute does not exist (the directory
+ "/sys/block/\*/device/duration_limits" does not exist).
+ Writing "1" to this file enables the use of command duration
+ limits for read and write commands in the kernel and turns on
+ the feature on the device. Writing "0" disables the feature.
+
+
+What: /sys/block/*/device/duration_limits/read/[1-7]/*
+Date: Dec, 2022
+KernelVersion: v6.3
+Contact: linux-scsi@vger.kernel.org
+Description:
+ (RO) For ATA and SCSI devices supporting the command duration
+ limits feature, this shows the set of 7 command duration limits
+ descriptors for read commands currently set on the device. For
+ each of the 7 descritors, the following read-only attributes
+ are present:
+
+ - duration_guideline: specifies the preferred length of time
+ in microseconds for the completion of a command.
+
+ - duration_guideline_policy: specifies the policy action
+ taken if the duration_guideline attribute specifies a
+ non-zero command duration guideline that the device is
+ unable to achieve for a command.
+
+ Possible values are:
+
+ - 0x0: The device will complete the command at the
+ earliest possible time consistent with the specified
+ command duration guideline.
+
+ - 0x1: If the specified command duration guideline has not
+ been achieved and the command duration guideline policy
+ field is not in the seventh command duration limits
+ descriptor, then the device continues processing that
+ command using the command duration limits descriptor
+ that has the next higher number.
+
+ - 0x2: The device will continue processing the command as
+ with no command duration limits descriptor being used.
+
+ - 0xD: The device will complete the command and an IO
+ failure will be reported to the user with the ETIME
+ error code.
+
+ - 0xF: Same as 0xD.
+
+ - max_active_time: specifies an upper limit in microseconds
+ on the time that elapses from the time at which the device
+ initiates actions to access, transfer, or act upon the
+ specified data until the time the device returns status for
+ the command.
+
+ - max_active_time_policy: specifies the policy action taken
+ if the time used to process a command exceeds a non-zero
+ time specified by the max_active_time attribute.
+
+ Possible values are:
+
+ - 0x0: The device will complete the command at the
+ earliest possible time (i.e, do nothing based on the max
+ time limit not being met).
+
+ - 0xD: The device will complete the command and an IO
+ failure will be reported to the user with the ETIME
+ error code.
+
+ - 0xE: Same as 0xD.
+
+ - 0xF: Same as 0xD.
+
+ - max_inactive_time: specifies an upper limit in microseconds
+ on the time that elapses from the time at which the device
+ receives the command until the time at which the device
+ initiates actions to access, transfer, or act upon the
+ specified data.
+
+ - max_inactive_time_policy: specifies the policy action taken
+ if a non-zero max_inactive_time limit is not met.
+
+ Possible values are:
+
+ - 0x0: The device will complete the command at the
+ earliest possible time (i.e, do nothing based on the max
+ time limit not being met).
+
+ - 0xD: The device will complete the command and an IO
+ failure will be reported to the user with the ETIME
+ error code.
+
+ - 0xF: Same as 0xD.
+
+
+What: /sys/block/*/device/duration_limits/read/page
+Date: Dec, 2022
+KernelVersion: v6.3
+Contact: linux-scsi@vger.kernel.org
+Description:
+ (RO) For ATA and SCSI devices supporting the command duration
+ limits feature, this shows the name of the device VPD page
+ specifying the set of 7 command duration limits descriptors for
+ read commands. Possible values are "T2A" and "T2B".
+
+
+What: /sys/block/*/device/duration_limits/write/[1-7]/*
+Date: Dec, 2022
+KernelVersion: v6.3
+Contact: linux-scsi@vger.kernel.org
+Description:
+ (RO) For ATA and SCSI devices supporting the command duration
+ limits feature, this shows the set of 7 command duration limits
+ descriptors for write commands currently set on the device. For
+ each of the 7 descritors, the same set of read-only attributes
+ as for read commands is present.
+
+
+What: /sys/block/*/device/duration_limits/write/page
+Date: Dec, 2022
+KernelVersion: v6.3
+Contact: linux-scsi@vger.kernel.org
+Description:
+ (RO) For ATA and SCSI devices supporting the command duration
+ limits feature, this shows the name of the device VPD page
+ specifying the set of 7 command duration limits descriptors for
+ write commands. Possible values are "T2A" and "T2B".
+
+
+What: /sys/block/*/device/duration_limits/perf_vs_duration_guideline
+Date: Dec, 2022
+KernelVersion: v6.3
+Contact: linux-scsi@vger.kernel.org
+Description:
+ (RO) For ATA and SCSI devices supporting the command duration
+ limits feature, this specifies the maximum percentage increase
+ in average command completion times (reduction in IOPS) that
+ is allowed for the device to perform actions based on the
+ contents of the duration guideline field in every command
+ duration limit descriptor for both read and write commands.
--
2.39.1