Re: [PATCH v5 3/4] ata: Enabling ATA Command Priorities

[Tejun Heo]

Hello,

On Thu, Oct 13, 2016 at 04:00:30PM -0700, Adam Manzanares wrote:
> 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 

Looks good to me.  Once the block changes are applied, I'll pull it
into libata tree and apply the ata part on top.

Thanks.

-- 
tejun
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[PATCH v5 3/4] 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 
---
 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 e207b33..18629e8 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -50,6 +50,7 @@
 #include 
 #include 
 #include 
+#include 
 
 #include "libata.h"
 #include "libata-transport.h"
@@ -1757,6 +1758,8 @@ 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;
@@ -1823,7 +1826,8 @@ 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 cla