From 106397376c0369fcc01c58dd189ff925a2724a57 Mon Sep 17 00:00:00 2001
From: David Jeffery <djeffery@redhat.com>
Date: Fri, 21 Jul 2023 17:57:15 +0800
Subject: [PATCH] sbitmap: fix batching wakeup
Git-commit: 106397376c0369fcc01c58dd189ff925a2724a57
Patch-mainline: v6.5-rc3
References: git-fixes
Current code supposes that it is enough to provide forward progress by
just waking up one wait queue after one completion batch is done.
Unfortunately this way isn't enough, cause waiter can be added to wait
queue just after it is woken up.
Follows one example(64 depth, wake_batch is 8)
1) all 64 tags are active
2) in each wait queue, there is only one single waiter
3) each time one completion batch(8 completions) wakes up just one
waiter in each wait queue, then immediately one new sleeper is added
to this wait queue
4) after 64 completions, 8 waiters are wakeup, and there are still 8
waiters in each wait queue
5) after another 8 active tags are completed, only one waiter can be
wakeup, and the other 7 can't be waken up anymore.
Turns out it isn't easy to fix this problem, so simply wakeup enough
waiters for single batch.
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20230721095715.232728-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
lib/sbitmap.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index eff4e42c425a..d0a5081dfd12 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -550,7 +550,7 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);
static void __sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
{
- int i, wake_index;
+ int i, wake_index, woken;
if (!atomic_read(&sbq->ws_active))
return;
@@ -567,13 +567,12 @@ static void __sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
*/
wake_index = sbq_index_inc(wake_index);
- /*
- * It is sufficient to wake up at least one waiter to
- * guarantee forward progress.
- */
- if (waitqueue_active(&ws->wait) &&
- wake_up_nr(&ws->wait, nr))
- break;
+ if (waitqueue_active(&ws->wait)) {
+ woken = wake_up_nr(&ws->wait, nr);
+ if (woken == nr)
+ break;
+ nr -= woken;
+ }
}
if (wake_index != atomic_read(&sbq->wake_index))
--
2.35.3