On Tue, Jul 3, 2018 at 4:37 AM, Jens Axboe <axboe@xxxxxxxxx> wrote:
> On 7/2/18 2:28 PM, Douglas Gilbert wrote:
>> On 2018-07-02 07:06 AM, Ming Lei wrote:
>>> With the introduced module parameter of 'use_blk_mq', it is easy
>>> to switch between 'blk_mq' and 'non_blk_mq' by reloading scsi_debug
>>> module, so that we can test scsi_mq/blk_mq related regressions easily.
>>>
>>> Cc: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
>>> Cc: Bart Van Assche <bart.vanassche@xxxxxxx>
>>> Cc: Jens Axboe <axboe@xxxxxxxxx>
>>> Cc: Omar Sandoval <osandov@xxxxxx>
>>> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
>>> ---
>>> drivers/scsi/scsi_debug.c | 5 +++++
>>> 1 file changed, 5 insertions(+)
>>>
>>> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
>>> index 24d7496cd9e2..236cfb669df3 100644
>>> --- a/drivers/scsi/scsi_debug.c
>>> +++ b/drivers/scsi/scsi_debug.c
>>> @@ -144,6 +144,7 @@ static const char *sdebug_version_date = "20180128";
>>> #define DEF_SUBMIT_QUEUES 1
>>> #define DEF_UUID_CTL 0
>>> #define JDELAY_OVERRIDDEN -9999
>>> +#define DEF_USE_BLK_MQ 0
>>>
>>> #define SDEBUG_LUN_0_VAL 0
>>>
>>> @@ -671,6 +672,7 @@ static bool sdebug_verbose;
>>> static bool have_dif_prot;
>>> static bool write_since_sync;
>>> static bool sdebug_statistics = DEF_STATISTICS;
>>> +static bool sdebug_use_blk_mq = DEF_USE_BLK_MQ;
>>>
>>> static unsigned int sdebug_store_sectors;
>>> static sector_t sdebug_capacity; /* in sectors */
>>> @@ -4537,6 +4539,7 @@ module_param_named(vpd_use_hostno, sdebug_vpd_use_hostno, int,
>>> S_IRUGO | S_IWUSR);
>>> module_param_named(write_same_length, sdebug_write_same_length, int,
>>> S_IRUGO | S_IWUSR);
>>> +module_param_named(use_blk_mq, sdebug_use_blk_mq, bool, S_IRUGO | S_IWUSR);
>>>
>>> MODULE_AUTHOR("Eric Youngdale + Douglas Gilbert");
>>> MODULE_DESCRIPTION("SCSI debug adapter driver");
>>> @@ -5849,6 +5852,8 @@ static int sdebug_driver_probe(struct device *dev)
>>> sdebug_driver_template.can_queue = sdebug_max_queue;
>>> if (sdebug_clustering)
>>> sdebug_driver_template.use_clustering = ENABLE_CLUSTERING;
>>> + if (sdebug_use_blk_mq)
>>> + sdebug_driver_template.force_blk_mq = 1;
>>> hpnt = scsi_host_alloc(&sdebug_driver_template, sizeof(sdbg_host));
>>> if (NULL == hpnt) {
>>> pr_err("scsi_host_alloc failed\n");
>>>
>>
>> Hi,
>> It is up to others whether this patch goes through. It seems the default
>> associated with blk_mq may soon change. So two things:
>> - I'd like to see a MODULE_PARM_DESC(use_blk_mq, ...) entry in patch
>> - perhaps a 3 valued use_blk_mq: 1 --> force blk_mq; 0 (def) --> accept
>> default mq setting; -1 --> turn off mq (if possible, if not it's a
>> NOP)
>
> The point is that the parameter is going to be short lived, since the
> non-mq path will be going away. We don't want drivers exposing this
> sort of thing, just to remove the option shortly again. Once we're
> happy with scsi-mq for a release or two, the old code should be
> deleted. Once that happens, then the option will have no purpose.
Not like other drivers, scsi_debug is a bit special, since it is for
test purpose. We may switch to scsi_mq at default soon, but the
whole MQ(block, scsi_mq) code may take ages to be removed,
maybe never.
We may use the per-driver parameter to test both mq and non-mq
path, especially for comparing both, then speed up to make MQ code
mature & stable. That is why I think this patch is very useful.
For example, we may write a test case to capture the recent scsi_mq
long boot delay regression easily with the introduced parameter.
Thanks,
Ming Lei
