On Sat, 2014-02-08 at 12:00 +0100, Bart Van Assche wrote:
> On 02/07/14 20:30, Nicholas A. Bellinger wrote:
> > All that scsi_debug with NOP'ed REQ_TYPE_FS commands is doing is calling
> > scsi_cmd->done() as soon as the descriptor has been dispatched into LLD
> > ->queuecommand() code.
> >
> > It's useful for determining an absolute performance ceiling between
> > scsi_mq vs. scsi_request_fn() based codepaths without involving any
> > other LLD specific overheads.
>
> Sorry but I'm not convinced that the scsi_debug driver is well suited
> for testing scsi-mq. In source file drivers/scsi/scsi_debug.c of kernel
> 3.14-rc1 I found the following:
>
> static DEF_SCSI_QCMD(scsi_debug_queuecommand)
>
> From include/scsi/scsi_host.h:
>
> /*
> * Temporary #define for host lock push down. Can be removed when all
> * drivers have been updated to take advantage of unlocked
> * queuecommand.
> *
> */
> #define DEF_SCSI_QCMD(func_name) \
> int func_name(struct Scsi_Host *shost, struct scsi_cmnd *cmd) \
> { \
> unsigned long irq_flags; \
> int rc; \
> spin_lock_irqsave(shost->host_lock, irq_flags); \
> scsi_cmd_get_serial(shost, cmd); \
> rc = func_name##_lck (cmd, cmd->scsi_done); \
> spin_unlock_irqrestore(shost->host_lock, irq_flags); \
> return rc; \
> }
>
> In other words, all scsi_debug_queuecommand() are serialized. I think
> for testing the scsi-mq code properly a SCSI LLD driver is needed that
> allows concurrent queuecommand() calls.
>
Again, try NOP'ing all REQ_TYPE_FS type commands immediately in
->queuecommand() in order to determine a baseline without any other LLD
overhead involved.
Here's what been used so far in target-pending/scsi-mq:
>From 0f312a951eedc87adc4c00adfec8ab317727efdd Mon Sep 17 00:00:00 2001
From: Nicholas Bellinger <n...@linux-iscsi.org>
Date: Fri, 24 May 2013 05:11:38 +0000
Subject: scsi-debug: Enable scsi-mq operation
v4 changes:
- Bump can_queue to 64 for performance testing
- Enable scsi-mq DIF support
- Add nop_fs_io module parameter for performance testing
Signed-off-by: Nicholas Bellinger <n...@linux-iscsi.org>
---
diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 80b8b10..612d36d 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -119,6 +119,7 @@ static const char * scsi_debug_version_date = "20100324";
#define DEF_VIRTUAL_GB 0
#define DEF_VPD_USE_HOSTNO 1
#define DEF_WRITESAME_LENGTH 0xFFFF
+#define DEF_NOP_FS_IO 0
/* bit mask values for scsi_debug_opts */
#define SCSI_DEBUG_OPT_NOISE 1
@@ -195,6 +196,7 @@ static unsigned int scsi_debug_unmap_max_blocks =
DEF_UNMAP_MAX_BLOCKS;
static unsigned int scsi_debug_unmap_max_desc = DEF_UNMAP_MAX_DESC;
static unsigned int scsi_debug_write_same_length = DEF_WRITESAME_LENGTH;
static bool scsi_debug_removable = DEF_REMOVABLE;
+static unsigned int scsi_debug_nop_fs_io = DEF_NOP_FS_IO;
static int scsi_debug_cmnd_count = 0;
@@ -2779,6 +2781,8 @@ module_param_named(vpd_use_hostno,
scsi_debug_vpd_use_hostno, int,
S_IRUGO | S_IWUSR);
module_param_named(write_same_length, scsi_debug_write_same_length, int,
S_IRUGO | S_IWUSR);
+module_param_named(nop_fs_io, scsi_debug_nop_fs_io, int,
+ S_IRUGO | S_IWUSR);
MODULE_AUTHOR("Eric Youngdale + Douglas Gilbert");
MODULE_DESCRIPTION("SCSI debug adapter driver");
@@ -2820,6 +2824,7 @@ MODULE_PARM_DESC(unmap_max_desc, "max # of ranges that
can be unmapped in one cm
MODULE_PARM_DESC(virtual_gb, "virtual gigabyte size (def=0 -> use
dev_size_mb)");
MODULE_PARM_DESC(vpd_use_hostno, "0 -> dev ids ignore hostno (def=1 -> unique
dev ids)");
MODULE_PARM_DESC(write_same_length, "Maximum blocks per WRITE SAME cmd
(def=0xffff)");
+MODULE_PARM_DESC(nop_fs_io, "Turn REQ_TYPE_FS I/O into NOPs");
static char sdebug_info[256];
@@ -3954,6 +3959,20 @@ write:
static DEF_SCSI_QCMD(scsi_debug_queuecommand)
+static int scsi_debug_queuecommand_mq(struct Scsi_Host *host, struct scsi_cmnd
*sc)
+{
+ struct request *rq = sc->request;
+
+ if (scsi_debug_nop_fs_io && rq->cmd_type == REQ_TYPE_FS) {
+ set_host_byte(sc, DID_OK);
+ sc->result |= SAM_STAT_GOOD;
+ sc->scsi_done(sc);
+ return 0;
+ }
+
+ return scsi_debug_queuecommand_lck(sc, sc->scsi_done);
+}
+
static struct scsi_host_template sdebug_driver_template = {
.show_info = scsi_debug_show_info,
.write_info = scsi_debug_write_info,
@@ -3965,6 +3984,8 @@ static struct scsi_host_template sdebug_driver_template =
{
.slave_destroy = scsi_debug_slave_destroy,
.ioctl = scsi_debug_ioctl,
.queuecommand = scsi_debug_queuecommand,
+ .queuecommand_mq = scsi_debug_queuecommand_mq,
+ .scsi_mq = true,
.eh_abort_handler = scsi_debug_abort,
.eh_bus_reset_handler = scsi_debug_bus_reset,
.eh_device_reset_handler = scsi_debug_device_reset,
@@ -3973,7 +3994,7 @@ static struct scsi_host_template sdebug_driver_template =
{
.can_queue = SCSI_DEBUG_CANQUEUE,
.this_id = 7,
.sg_tablesize = 256,
- .cmd_per_lun = 16,
+ .cmd_per_lun = 64,
.max_sectors = 0xffff,
.use_clustering = DISABLE_CLUSTERING,
.module = THIS_MODULE,
--
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