[PATCH] scsi: add a CONFIG_SCSI_MQ_DEFAULT option

[Christoph Hellwig]

Add a Kconfig option to enable the blk-mq path for SCSI by default
to ease testing and deployment in setups that know they benefit
from blk-mq.

Signed-off-by: Christoph Hellwig <***@lst.de>
---
drivers/scsi/Kconfig | 11 +++++++++++
drivers/scsi/scsi.c | 4 ++++
2 files changed, 15 insertions(+)

diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
index 18a3358..71b0877 100644
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -45,6 +45,17 @@ config SCSI_NETLINK
default n
select NET

+config SCSI_MQ_DEFAULT
+ bool "SCSI: use blk-mq I/O path by default"
+ depends on SCSI
+ ---help---
+ This option enables the new blk-mq based I/O path for SCSI
+ devices by default. With the option the scsi_mod.use_blk_mq
+ module/boot option defaults to Y, without it to N, but it can
+ still be overriden either way.
+
+ If unsure say N.
+
config SCSI_PROC_FS
bool "legacy /proc/scsi/ support"
depends on SCSI && PROC_FS
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 1423cb1..79c77b4 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -1367,7 +1367,11 @@ MODULE_LICENSE("GPL");
module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");

+#ifdef CONFIG_SCSI_MQ_DEFAULT
+bool scsi_use_blk_mq = true;
+#else
bool scsi_use_blk_mq = false;
+#endif
module_param_named(use_blk_mq, scsi_use_blk_mq, bool, S_IWUSR | S_IRUGO);

static int __init init_scsi(void)

[Martin K. Petersen]

Christoph> Add a Kconfig option to enable the blk-mq path for SCSI by
Christoph> default to ease testing and deployment in setups that know
Christoph> they benefit from blk-mq.

Looks OK to me.

Reviewed-by: Martin K. Petersen <***@oracle.com>

[Elliott, Robert (Server Storage)]

-----Original Message-----

...

Add a Kconfig option to enable the blk-mq path for SCSI by default
to ease testing and deployment in setups that know they benefit
from blk-mq.

...

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 1423cb1..79c77b4 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -1367,7 +1367,11 @@ MODULE_LICENSE("GPL");
module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");
+#ifdef CONFIG_SCSI_MQ_DEFAULT
+bool scsi_use_blk_mq = true;
+#else
bool scsi_use_blk_mq = false;
+#endif
module_param_named(use_blk_mq, scsi_use_blk_mq, bool, S_IWUSR | S_IRUGO);
static int __init init_scsi(void)

A printk indicating the choice would be helpful; there's no indication
in the "Command line" or "Kernel command line" lines after this patch.

Reviewed-by: Robert Elliott <***@hp.com>
Tested-by: Robert Elliott <***@hp.com>

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[Christoph Hellwig]

Post by Elliott, Robert (Server Storage)
A printk indicating the choice would be helpful; there's no indication
in the "Command line" or "Kernel command line" lines after this patch.

No need for a printk to further increase the gigantic kernel log at boot
time, you can easily find the indicator in the use_blk_mq sysfs attributes,
both on the module, and each individual host.
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