[PATCH 0/3] Enabling ATA Command Priorities

[PATCH 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.

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

 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/libata.h    | 27 +++++++++++++++++
 6 files changed, 142 insertions(+), 3 deletions(-)

-- 
2.1.4

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[PATCH 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.

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

 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/libata.h    | 27 +++++++++++++++++
 6 files changed, 142 insertions(+), 3 deletions(-)

-- 
2.1.4

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

[Adam Manzanares]

Patch adds association between iocontext and a request.

Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
---
 block/blk-core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 36c7ac3..9c6d733 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -33,6 +33,7 @@
 #include <linux/ratelimit.h>
 #include <linux/pm_runtime.h>
 #include <linux/blk-cgroup.h>
+#include <linux/ioprio.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/block.h>
@@ -1648,6 +1649,7 @@ out:
 
 void init_request_from_bio(struct request *req, struct bio *bio)
 {
+	struct io_context *ioc = rq_ioc(bio);
 	req->cmd_type = REQ_TYPE_FS;
 
 	req->cmd_flags |= bio->bi_opf & REQ_COMMON_MASK;
@@ -1657,6 +1659,9 @@ 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 (ioc)
+		req->ioprio = ioprio_best(req->ioprio, ioc->ioprio);
+
 	blk_rq_bio_prep(req->q, req, bio);
 }
 
-- 
2.1.4

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This e-mail and any files transmitted with it may contain confidential or legally privileged information of WDC and/or its affiliates, and are intended solely for the use of the individual or entity to which they are addressed. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited. If you have received this e-mail in error, please notify the sender immediately and delete the e-mail in its entirety from your system.

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

[Adam Manzanares]

Patch adds association between iocontext and a request.

Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
---
 block/blk-core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 36c7ac3..9c6d733 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -33,6 +33,7 @@
 #include <linux/ratelimit.h>
 #include <linux/pm_runtime.h>
 #include <linux/blk-cgroup.h>
+#include <linux/ioprio.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/block.h>
@@ -1648,6 +1649,7 @@ out:
 
 void init_request_from_bio(struct request *req, struct bio *bio)
 {
+	struct io_context *ioc = rq_ioc(bio);
 	req->cmd_type = REQ_TYPE_FS;
 
 	req->cmd_flags |= bio->bi_opf & REQ_COMMON_MASK;
@@ -1657,6 +1659,9 @@ 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 (ioc)
+		req->ioprio = ioprio_best(req->ioprio, ioc->ioprio);
+
 	blk_rq_bio_prep(req->q, req, bio);
 }
 
-- 
2.1.4

[PATCH 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.

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    | 19 +++++++++++++++++++
 5 files changed, 65 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 <linux/uaccess.h>
 #include <linux/suspend.h>
 #include <asm/unaligned.h>
+#include <linux/ioprio.h>
 
 #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 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 adbc812..ebe4c3b 100644
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -347,6 +347,7 @@ 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,
@@ -897,6 +898,11 @@ 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 e37d4f9..a3c66852 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -165,6 +165,7 @@ 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),
@@ -341,7 +342,9 @@ 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,
 
@@ -1609,6 +1612,22 @@ 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_PIO | ATA_DFLAG_NCQ_OFF |
+			      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

Western Digital Corporation (and its subsidiaries) E-mail Confidentiality Notice & Disclaimer:

This e-mail and any files transmitted with it may contain confidential or legally privileged information of WDC and/or its affiliates, and are intended solely for the use of the individual or entity to which they are addressed. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited. If you have received this e-mail in error, please notify the sender immediately and delete the e-mail in its entirety from your system.

[PATCH 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.

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    | 19 +++++++++++++++++++
 5 files changed, 65 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 <linux/uaccess.h>
 #include <linux/suspend.h>
 #include <asm/unaligned.h>
+#include <linux/ioprio.h>
 
 #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 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 adbc812..ebe4c3b 100644
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -347,6 +347,7 @@ 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,
@@ -897,6 +898,11 @@ 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 e37d4f9..a3c66852 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -165,6 +165,7 @@ 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),
@@ -341,7 +342,9 @@ 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,
 
@@ -1609,6 +1612,22 @@ 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_PIO | ATA_DFLAG_NCQ_OFF |
+			      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

[PATCH 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    |  8 ++++++
 4 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index dcf2c72..383adf7 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_enable_prio,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ahci_sdev_attrs);
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 181b530..d0cf987 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_prio_enabled(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 18629e8..10ba118 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_enable_prio_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 enable_prio;
+
+	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;
+	}
+
+	enable_prio = ata_prio_enabled(dev);
+
+unlock:
+	spin_unlock_irq(ap->lock);
+
+	return rc ? rc : snprintf(buf, 20, "%u\n", enable_prio);
+}
+
+static ssize_t ata_enable_prio_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_ENABLE_PRIO;
+	else
+		dev->flags &= ~ATA_DFLAG_ENABLE_PRIO;
+
+unlock:
+	spin_unlock_irqrestore(ap->lock, flags);
+
+	return rc ? rc : len;
+}
+
+DEVICE_ATTR(enable_prio, S_IRUGO | S_IWUSR,
+	    ata_enable_prio_show, ata_enable_prio_store);
+EXPORT_SYMBOL_GPL(dev_attr_enable_prio);
+
 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_enable_prio,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ata_common_sdev_attrs);
diff --git a/include/linux/libata.h b/include/linux/libata.h
index a3c66852..804c4c6 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -166,6 +166,7 @@ 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_ENABLE_PRIO	= (1 << 21), /* User enable device priority */
 	ATA_DFLAG_INIT_MASK	= (1 << 24) - 1,
 
 	ATA_DFLAG_DETACH	= (1 << 24),
@@ -544,6 +545,7 @@ 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_enable_prio;
 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 +1630,12 @@ static inline int ata_ncq_prio_enabled(struct ata_device *dev)
 			      ATA_DFLAG_NCQ_PRIO)) == ATA_DFLAG_NCQ_PRIO;
 }
 
+static inline int ata_prio_enabled(struct ata_device *dev)
+{
+	return ((dev->flags & ATA_DFLAG_ENABLE_PRIO) ==
+		 ATA_DFLAG_ENABLE_PRIO);
+}
+
 static inline bool ata_fpdma_dsm_supported(struct ata_device *dev)
 {
 	return (dev->flags & ATA_DFLAG_NCQ_SEND_RECV) &&
-- 
2.1.4

[PATCH 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    |  8 ++++++
 4 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index dcf2c72..383adf7 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_enable_prio,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ahci_sdev_attrs);
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 181b530..d0cf987 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_prio_enabled(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 18629e8..10ba118 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_enable_prio_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 enable_prio;
+
+	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;
+	}
+
+	enable_prio = ata_prio_enabled(dev);
+
+unlock:
+	spin_unlock_irq(ap->lock);
+
+	return rc ? rc : snprintf(buf, 20, "%u\n", enable_prio);
+}
+
+static ssize_t ata_enable_prio_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_ENABLE_PRIO;
+	else
+		dev->flags &= ~ATA_DFLAG_ENABLE_PRIO;
+
+unlock:
+	spin_unlock_irqrestore(ap->lock, flags);
+
+	return rc ? rc : len;
+}
+
+DEVICE_ATTR(enable_prio, S_IRUGO | S_IWUSR,
+	    ata_enable_prio_show, ata_enable_prio_store);
+EXPORT_SYMBOL_GPL(dev_attr_enable_prio);
+
 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_enable_prio,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ata_common_sdev_attrs);
diff --git a/include/linux/libata.h b/include/linux/libata.h
index a3c66852..804c4c6 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -166,6 +166,7 @@ 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_ENABLE_PRIO	= (1 << 21), /* User enable device priority */
 	ATA_DFLAG_INIT_MASK	= (1 << 24) - 1,
 
 	ATA_DFLAG_DETACH	= (1 << 24),
@@ -544,6 +545,7 @@ 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_enable_prio;
 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 +1630,12 @@ static inline int ata_ncq_prio_enabled(struct ata_device *dev)
 			      ATA_DFLAG_NCQ_PRIO)) == ATA_DFLAG_NCQ_PRIO;
 }
 
+static inline int ata_prio_enabled(struct ata_device *dev)
+{
+	return ((dev->flags & ATA_DFLAG_ENABLE_PRIO) ==
+		 ATA_DFLAG_ENABLE_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 0/3] Enabling ATA Command Priorities

[Christoph Hellwig]

The series looks fine to me:

Reviewed-by: Christoph Hellwig <hch@lst.de>

The only question is if we need to bother with the last patch to
make the feature conditional at all, given that we both need hardware
support and applications opting into using I/O priorities to even use
it.  But if you feel it's safer that way the unable certainly doesn't
hurt.

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

[Adam Manzanares]

SSBwcmVmZXIgaGF2aW5nIHRoZSBmZWF0dXJlIGNvbmRpdGlvbmFsIHNvIHlvdSBjYW4gdXNlIHRo
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eSBmcm9tIHlvdXIgc3lzdGVtLgo=

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

[Adam Manzanares]

I prefer having the feature conditional so you can use the CFQ scheduler with I/O priorities as is. If you decide to enable the feature then the priorities will be passed down to the drive in addition to the work that the CFQ scheduler does. Since this feature may change the user perceived performance of the device I want to make sure they know what they are getting into.





On 9/27/16, 7:06 PM, "Christoph Hellwig" <hch@infradead.org> wrote:

>The series looks fine to me:
>
>Reviewed-by: Christoph Hellwig <hch@lst.de>
>
>The only question is if we need to bother with the last patch to
>make the feature conditional at all, given that we both need hardware
>support and applications opting into using I/O priorities to even use
>it.  But if you feel it's safer that way the unable certainly doesn't
>hurt.

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

[Tejun Heo]

Hello,

On Tue, Sep 27, 2016 at 11:14:54AM -0700, Adam Manzanares wrote:
> Patch adds association between iocontext and a request.
> 
> Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>

Can you please describe how this may impact existing usages?

Thanks.

-- 
tejun

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

[Tejun Heo]

Hello,

On Tue, Sep 27, 2016 at 11:14:55AM -0700, Adam Manzanares wrote:
> +/**
> + *	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_PIO | ATA_DFLAG_NCQ_OFF |
> +			      ATA_DFLAG_NCQ_PRIO)) == ATA_DFLAG_NCQ_PRIO;

I'm not sure this needs to test PIO and NCQ_OFF.  This functions
pretty much can assume that it'd be only called in NCQ context, no?

Thanks.

-- 
tejun

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

[tj]

Hello,

On Wed, Sep 28, 2016 at 03:43:32AM +0000, Adam Manzanares wrote:
> I prefer having the feature conditional so you can use the CFQ
> scheduler with I/O priorities as is. If you decide to enable the
> feature then the priorities will be passed down to the drive in
> addition to the work that the CFQ scheduler does. Since this feature
> may change the user perceived performance of the device I want to
> make sure they know what they are getting into.

Yeah, I prefer to have it behind an explicit flag given the history of
optional ATA features.  The feature is unlikely to matter to a lot of
people and is almost bound to break existing RT prio usages.

Thanks.

-- 
tejun

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

[Adam Manzanares]

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

[Adam Manzanares]

Hello Tejun,

The 09/29/2016 10:40, Tejun Heo wrote:
> Hello,
> 
> On Tue, Sep 27, 2016 at 11:14:54AM -0700, Adam Manzanares wrote:
> > Patch adds association between iocontext and a request.
> > 
> > Signed-off-by: Adam Manzanares <adam.manzanares@hgst.com>
> 
> Can you please describe how this may impact existing usages?
>
I'll start with the changes I made and work my way through a grep of            
ioprio. Please add or correct any of the assumptions I have made.               
                                                                                
In blk-core, the behavior before the patch is to get the ioprio for the request 
from the bio. The only references I found to bio_set_prio are in bcache. Both   
of these references are in low priority operations (gc, bg writeback) so the    
iopriority of the bio is set to IO_PRIOCLASS_IDLE in these cases.               
                                                                                
A kernel thread is used to submit these bios so the ioprio is going to come     
from the current running task if the iocontext exists. This could be a problem  
if we have set a task with high priority and some background work ends up       
getting generated in the bcache layer. I propose that we check if the           
iopriority of the bio is valid and if so, then we keep the priorirty from the   
bio.                                                                            
                                                                                
The second area that I see a potential problem is in the merging code code in   
blk-core when a bio is queued. If there is a request that is mergeable then     
the merge code takes the highest priority of the bio and the request. This      
could wipe out the values set by bio_set_prio. I think it would be              
best to set the request as non mergeable when we see that it is a high          
priority IO request.                                                            
                                                                                
The third area that is of interest is in the CFQ scheduler and the ioprio is    
only used in the case of async IO and I found that the priority is only         
obtained from the task and not from the request. This leads me to believe that  
the changes made in the blk-core to add the priority to the request will not    
impact the CFQ scheduler. 

The fourth area that might be concerning is the drivers. virtio_block copies    
the request priority into a virtual block request. I am assuming that this      
eventually makes it to another device driver so we don't need to worry about    
this. null block device driver also uses the ioprio, but this is also not a     
concern. lightnvm also sets the ioprio to build a request that is passed onto   
another driver. The last driver that uses the request ioprio is the fusion      
mptsas driver and I don't understand how it is using the ioprio. From what I    
can tell it is taking a request of IOPRIO_CLASS_NONE with data of 0x7 and       
calling this high priority IO. This could be impacted by the code I have        
proposed, but I believe the authors intended to treat this particular ioprio    
value as high priority. The driver will pass the request to the device          
with high priority if the appropriate ioprio values is seen on the request.     
                                                                                
The fifth area that I noticed may be impacted is file systems. btrfs uses low   
priority IO for read ahead. Ext4 uses ioprio for journaling. Both of these      
issues are not a problem because the ioprio is set on the task and not on a     
bio.

> Thanks.
> 
> -- 
> tejun

Take care,
Adam

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

[Adam Manzanares]

The 09/29/2016 10:45, Tejun Heo wrote:
> Hello,
> 
> On Tue, Sep 27, 2016 at 11:14:55AM -0700, Adam Manzanares wrote:
> > +/**
> > + *	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_PIO | ATA_DFLAG_NCQ_OFF |
> > +			      ATA_DFLAG_NCQ_PRIO)) == ATA_DFLAG_NCQ_PRIO;
> 
> I'm not sure this needs to test PIO and NCQ_OFF.  This functions
> pretty much can assume that it'd be only called in NCQ context, no?
>

This should only be called in the NCQ context so these checks are redundant
I'll clean this up in the next version of the patches.

> Thanks.
> 
> -- 
> tejun

Take care,
Adam

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

[Adam Manzanares]

The 09/29/2016 10:45, Tejun Heo wrote:
> Hello,
> 
> On Tue, Sep 27, 2016 at 11:14:55AM -0700, Adam Manzanares wrote:
> > +/**
> > + *	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_PIO | ATA_DFLAG_NCQ_OFF |
> > +			      ATA_DFLAG_NCQ_PRIO)) == ATA_DFLAG_NCQ_PRIO;
> 
> I'm not sure this needs to test PIO and NCQ_OFF.  This functions
> pretty much can assume that it'd be only called in NCQ context, no?
>

This should only be called in the NCQ context so these checks are redundant
I'll clean this up in the next version of the patches.

> Thanks.
> 
> -- 
> tejun

Take care,
Adam

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

[Tejun Heo]

Hello, Adam.

On Fri, Sep 30, 2016 at 09:02:17AM -0700, Adam Manzanares wrote:
> I'll start with the changes I made and work my way through a grep of            
> ioprio. Please add or correct any of the assumptions I have made.               

Well, it looks like you're the one who's most familiar with ioprio
handling at this point. :)

> In blk-core, the behavior before the patch is to get the ioprio for the request 
> from the bio. The only references I found to bio_set_prio are in bcache. Both   
> of these references are in low priority operations (gc, bg writeback) so the    
> iopriority of the bio is set to IO_PRIOCLASS_IDLE in these cases.               
>                                                                                 
> A kernel thread is used to submit these bios so the ioprio is going to come     
> from the current running task if the iocontext exists. This could be a problem  
> if we have set a task with high priority and some background work ends up       
> getting generated in the bcache layer. I propose that we check if the           
> iopriority of the bio is valid and if so, then we keep the priorirty from the   
> bio.                                                                            

I wonder whether the right thing to do is adding bio->bi_ioprio which
is initialized on bio submission and carried through req->ioprio.

> The second area that I see a potential problem is in the merging code code in   
> blk-core when a bio is queued. If there is a request that is mergeable then     
> the merge code takes the highest priority of the bio and the request. This      
> could wipe out the values set by bio_set_prio. I think it would be              
> best to set the request as non mergeable when we see that it is a high          
> priority IO request.                                                            

The current behavior should be fine for most non-pathological cases
but I have no objection to not merging ios with differing priorities.

> The third area that is of interest is in the CFQ scheduler and the ioprio is    
> only used in the case of async IO and I found that the priority is only         
> obtained from the task and not from the request. This leads me to believe that  
> the changes made in the blk-core to add the priority to the request will not    
> impact the CFQ scheduler. 
>
> The fourth area that might be concerning is the drivers. virtio_block copies    
> the request priority into a virtual block request. I am assuming that this      
> eventually makes it to another device driver so we don't need to worry about    
> this. null block device driver also uses the ioprio, but this is also not a     
> concern. lightnvm also sets the ioprio to build a request that is passed onto   
> another driver. The last driver that uses the request ioprio is the fusion      
> mptsas driver and I don't understand how it is using the ioprio. From what I    
> can tell it is taking a request of IOPRIO_CLASS_NONE with data of 0x7 and       
> calling this high priority IO. This could be impacted by the code I have        
> proposed, but I believe the authors intended to treat this particular ioprio    
> value as high priority. The driver will pass the request to the device          
> with high priority if the appropriate ioprio values is seen on the request.     
>                                                                                 
> The fifth area that I noticed may be impacted is file systems. btrfs uses low   
> priority IO for read ahead. Ext4 uses ioprio for journaling. Both of these      
> issues are not a problem because the ioprio is set on the task and not on a     
> bio.

Yeah, looks good to me.  Care to include a brief summary of expected
(non)impacts in the patch description?

Thanks.

-- 
tejun

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

[Adam Manzanares]

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

[Adam Manzanares]

Hello Tejun,

10/02/2016 10:53, Tejun Heo wrote:
> Hello, Adam.
> 
> On Fri, Sep 30, 2016 at 09:02:17AM -0700, Adam Manzanares wrote:
> > I'll start with the changes I made and work my way through a grep of            
> > ioprio. Please add or correct any of the assumptions I have made.               
> 
> Well, it looks like you're the one who's most familiar with ioprio
> handling at this point. :)
> 
> > In blk-core, the behavior before the patch is to get the ioprio for the request 
> > from the bio. The only references I found to bio_set_prio are in bcache. Both   
> > of these references are in low priority operations (gc, bg writeback) so the    
> > iopriority of the bio is set to IO_PRIOCLASS_IDLE in these cases.               
> >                                                                                 
> > A kernel thread is used to submit these bios so the ioprio is going to come     
> > from the current running task if the iocontext exists. This could be a problem  
> > if we have set a task with high priority and some background work ends up       
> > getting generated in the bcache layer. I propose that we check if the           
> > iopriority of the bio is valid and if so, then we keep the priorirty from the   
> > bio.                                                                            
> 
> I wonder whether the right thing to do is adding bio->bi_ioprio which
> is initialized on bio submission and carried through req->ioprio.
> 

I looked around and thought about this and I'm not sure if this will help. 
I dug into the bio submission code and I thought generic_make_request was 
the best place to save the ioprio information. This is quite close in 
the call stack to init_request_from bio. Bcache sets the bio priority before 
the submission, so we would have to check to see if the bio priority was 
valid on bio submission leaving us with the same problem. Leaving the 
priority in the upper bits of bio->bi_rw is fine with me. It may help to 
have the bio->bi_ioprio for clarity, but I think we will still face the 
issue of having to check if this value is set when we submit the bio or 
init the request so I'm leaning towards leaving it as is.


> > The second area that I see a potential problem is in the merging code code in   
> > blk-core when a bio is queued. If there is a request that is mergeable then     
> > the merge code takes the highest priority of the bio and the request. This      
> > could wipe out the values set by bio_set_prio. I think it would be              
> > best to set the request as non mergeable when we see that it is a high          
> > priority IO request.                                                            
> 
> The current behavior should be fine for most non-pathological cases
> but I have no objection to not merging ios with differing priorities.
> 
> > The third area that is of interest is in the CFQ scheduler and the ioprio is    
> > only used in the case of async IO and I found that the priority is only         
> > obtained from the task and not from the request. This leads me to believe that  
> > the changes made in the blk-core to add the priority to the request will not    
> > impact the CFQ scheduler. 
> >
> > The fourth area that might be concerning is the drivers. virtio_block copies    
> > the request priority into a virtual block request. I am assuming that this      
> > eventually makes it to another device driver so we don't need to worry about    
> > this. null block device driver also uses the ioprio, but this is also not a     
> > concern. lightnvm also sets the ioprio to build a request that is passed onto   
> > another driver. The last driver that uses the request ioprio is the fusion      
> > mptsas driver and I don't understand how it is using the ioprio. From what I    
> > can tell it is taking a request of IOPRIO_CLASS_NONE with data of 0x7 and       
> > calling this high priority IO. This could be impacted by the code I have        
> > proposed, but I believe the authors intended to treat this particular ioprio    
> > value as high priority. The driver will pass the request to the device          
> > with high priority if the appropriate ioprio values is seen on the request.     
> >                                                                                 
> > The fifth area that I noticed may be impacted is file systems. btrfs uses low   
> > priority IO for read ahead. Ext4 uses ioprio for journaling. Both of these      
> > issues are not a problem because the ioprio is set on the task and not on a     
> > bio.
> 
> Yeah, looks good to me.  Care to include a brief summary of expected
> (non)impacts in the patch description?
> 
I'm going to send out an updated series of patches summarizing some of this 
discussion and I'll also include some performance results that we have 
measured.

> Thanks.
> 
> -- 
> tejun

Take care,
Adam

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

[Tejun Heo]

Hello, Adam.

On Tue, Oct 04, 2016 at 08:49:18AM -0700, Adam Manzanares wrote:
> > I wonder whether the right thing to do is adding bio->bi_ioprio which
> > is initialized on bio submission and carried through req->ioprio.
> 
> I looked around and thought about this and I'm not sure if this will help. 
> I dug into the bio submission code and I thought generic_make_request was 
> the best place to save the ioprio information. This is quite close in 
> the call stack to init_request_from bio. Bcache sets the bio priority before 
> the submission, so we would have to check to see if the bio priority was 
> valid on bio submission leaving us with the same problem. Leaving the 
> priority in the upper bits of bio->bi_rw is fine with me. It may help to 
> have the bio->bi_ioprio for clarity, but I think we will still face the 
> issue of having to check if this value is set when we submit the bio or 
> init the request so I'm leaning towards leaving it as is.

I see.  Thanks for looking into it.  It's icky that we don't have a
clear path of propagating ioprio but let's save that for another day.

-- 
tejun