Messages in this thread | | | Subject | Re: [PATCH -next RFC v2 8/8] sbitmap: wake up the number of threads based on required tags | From | "yukuai (C)" <> | Date | Sat, 9 Apr 2022 10:19:32 +0800 |
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在 2022/04/08 22:31, Bart Van Assche 写道: > 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? Hi,
That is a race condition, I was hoping that the problem patch 5 fixed can cover this.
Thanks, Kuai > > Thanks, > > Bart. > . >
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