Messages in this thread | | | Date | Fri, 8 Apr 2022 07:31:02 -0700 | Subject | Re: [PATCH -next RFC v2 8/8] sbitmap: wake up the number of threads based on required tags | From | Bart Van Assche <> |
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On 4/8/22 00:39, Yu Kuai wrote: > Always wake up 'wake_batch' threads will intensify competition and > split io won't be issued continuously. Now that how many tags is required > is recorded for huge io, it's safe to wake up baed on required tags. > > Signed-off-by: Yu Kuai <yukuai3@huawei.com> > --- > lib/sbitmap.c | 22 +++++++++++++++++++++- > 1 file changed, 21 insertions(+), 1 deletion(-) > > diff --git a/lib/sbitmap.c b/lib/sbitmap.c > index 8d01e02ea4b1..eac9fa5c2b4d 100644 > --- a/lib/sbitmap.c > +++ b/lib/sbitmap.c > @@ -614,6 +614,26 @@ static inline void sbq_update_preemption(struct sbitmap_queue *sbq, > WRITE_ONCE(sbq->force_tag_preemption, force); > } > > +static unsigned int get_wake_nr(struct sbq_wait_state *ws, unsigned int nr_tags)
Consider renaming "get_wake_nr()" into "nr_to_wake_up()".
> +{ > + struct sbq_wait *wait; > + struct wait_queue_entry *entry; > + unsigned int nr = 1; > + > + spin_lock_irq(&ws->wait.lock); > + list_for_each_entry(entry, &ws->wait.head, entry) { > + wait = container_of(entry, struct sbq_wait, wait); > + if (nr_tags <= wait->nr_tags) > + break; > + > + nr++; > + nr_tags -= wait->nr_tags; > + } > + spin_unlock_irq(&ws->wait.lock); > + > + return nr; > +} > + > static bool __sbq_wake_up(struct sbitmap_queue *sbq) > { > struct sbq_wait_state *ws; > @@ -648,7 +668,7 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq) > smp_mb__before_atomic(); > atomic_set(&ws->wait_cnt, wake_batch); > sbq_update_preemption(sbq, wake_batch); > - wake_up_nr(&ws->wait, wake_batch); > + wake_up_nr(&ws->wait, get_wake_nr(ws, wake_batch)); > > return true; > }
ws->wait.lock is unlocked after the number of threads to wake up has been computed and is locked again by wake_up_nr(). The ws->wait.head list may be modified after get_wake_nr() returns and before wake_up_nr() is called. Isn't that a race condition?
Thanks,
Bart.
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