Re: [PATCH] null_blk: add "no_sched" module parameter

[weiping zhang <zhangweiping@didichuxing.com>]

On Fri, Sep 29, 2017 at 11:39:03PM +0200, Jens Axboe wrote:
> On 09/29/2017 07:09 PM, weiping zhang wrote:
> > add an option that disable io scheduler for null block device.
> > 
> > Signed-off-by: weiping zhang <zhangweiping@didichuxing.com>
> > ---
> >  drivers/block/null_blk.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
> > index bd92286..3c63863 100644
> > --- a/drivers/block/null_blk.c
> > +++ b/drivers/block/null_blk.c
> > @@ -154,6 +154,10 @@ enum {
> >  	NULL_Q_MQ		= 2,
> >  };
> >  
> > +static int g_no_sched;
> > +module_param_named(no_sched, g_no_sched, int, S_IRUGO);
> > +MODULE_PARM_DESC(no_sched, "No io scheduler");
> > +
> >  static int g_submit_queues = 1;
> >  module_param_named(submit_queues, g_submit_queues, int, S_IRUGO);
> >  MODULE_PARM_DESC(submit_queues, "Number of submission queues");
> > @@ -1753,7 +1757,7 @@ static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
> >  						g_hw_queue_depth;
> >  	set->numa_node = nullb ? nullb->dev->home_node : g_home_node;
> >  	set->cmd_size	= sizeof(struct nullb_cmd);
> > -	set->flags = BLK_MQ_F_SHOULD_MERGE;
> > +	set->flags = g_no_sched ? BLK_MQ_F_NO_SCHED : BLK_MQ_F_SHOULD_MERGE;
> 
> This should be:
> 
> 	set->flags = BLK_MQ_F_SHOULD_MERGE;
> 	if (g_no_sched)
> 		set->flags |= BLK_MQ_F_NO_SCHED;
> 
That's right, I go through these two flags, if no io scheduler,
BLK_MQ_F_SHOULD_MERGE can make sw ctx merge happen. I will send V2.

Thanks
weiping