Re: wbt_lat_usec still set despite wbt disabled by BFQ

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

在 2022/09/14 14:05, Holger Hoffstätte 写道:
> On 2022-09-14 03:35, Yu Kuai wrote:
> [snip]
> > Thanks for the test, it turns out this way doesn't select bfq as default
> > as I expected...
> >
> > wbt can show min_lat_nsec despite that wbt can be disabled by
> > wbt_disable_default(), I do miss that previously...
> >
> > Can you try the following patch again?
> >
> > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> > index a630d657c054..3e8adb95ff02 100644
> > --- a/block/blk-sysfs.c
> > +++ b/block/blk-sysfs.c
> > @@ -467,10 +467,14 @@ static ssize_t queue_io_timeout_store(struct 
> > request_queue *q, const char *page,
> >
> >   static ssize_t queue_wb_lat_show(struct request_queue *q, char *page)
> >   {
> > +       u64 lat;
> > +
> >          if (!wbt_rq_qos(q))
> >                  return -EINVAL;
> >
> > -       return sprintf(page, "%llu\n", div_u64(wbt_get_min_lat(q), 
> > 1000));
> > +       lat = wbt_disabled(q) ? 0 : div_u64(wbt_get_min_lat(q), 1000);
> > +
> > +       return sprintf(page, "%llu\n", lat);
> >   }
> >
> >   static ssize_t queue_wb_lat_store(struct request_queue *q, const 
> > char *page,
> > @@ -493,6 +497,9 @@ static ssize_t queue_wb_lat_store(struct 
> > request_queue *q, const char *page,
> >                          return ret;
> >          }
> >
> > +       if (wbt_disabled(q))
> > +               return -EINVAL;
> > +
> >          if (val == -1)
> >                  val = wbt_default_latency_nsec(q);
> >          else if (val >= 0)
> > diff --git a/block/blk-wbt.c b/block/blk-wbt.c
> > index 26ee6ca66a93..55d1015ef117 100644
> > --- a/block/blk-wbt.c
> > +++ b/block/blk-wbt.c
> > @@ -423,6 +423,13 @@ static void wbt_update_limits(struct rq_wb *rwb)
> >          rwb_wake_all(rwb);
> >   }
> >
> > +bool wbt_disabled(struct request_queue *q)
> > +{
> > +       struct rq_qos *rqos = wbt_rq_qos(q);
> > +
> > +       return !rqos || RQWB(rqos)->enable_state == 
> > WBT_STATE_OFF_DEFAULT;
> > +}
> > +
> >   u64 wbt_get_min_lat(struct request_queue *q)
> >   {
> >          struct rq_qos *rqos = wbt_rq_qos(q);
> > diff --git a/block/blk-wbt.h b/block/blk-wbt.h
> > index 1a49b6ac397c..4252b8077257 100644
> > --- a/block/blk-wbt.h
> > +++ b/block/blk-wbt.h
> > @@ -94,6 +94,7 @@ void wbt_enable_default(struct request_queue *, bool);
> >
> >   u64 wbt_get_min_lat(struct request_queue *q);
> >   void wbt_set_min_lat(struct request_queue *q, u64 val);
> > +bool wbt_disabled(struct request_queue *);
> >
> >   void wbt_set_write_cache(struct request_queue *, bool);
>
> This one works! :)
>
> After boot:
>
> $cat /sys/block/sdc/queue/scheduler
> mq-deadline [bfq] none
> $cat /sys/block/sdc/queue/wbt_lat_usec
> 0
>
> Changing schedulers  back and forth - here on a device with different
> default - also works:
>
> $cat /sys/block/sda/queue/scheduler
> [mq-deadline] bfq none
> $cat /sys/block/sda/queue/wbt_lat_usec
> 2000
> $echo bfq > /sys/block/sda/queue/scheduler
> $cat /sys/block/sda/queue/wbt_lat_usec
> 0
> $echo deadline > /sys/block/sda/queue/scheduler
> $cat /sys/block/sda/queue/wbt_lat_usec
> 2000
>
> Feel free to add my Reported-by and Tested-by.
I'll send a patch soon. Thanks again for the test.

Kuai
> cheers!
> Holger
>
> .