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From: Gabriel Krisman Bertazi <krisman@suse.de>
To: Kemeng Shi <shikemeng@huawei.com>
Cc: <axboe@kernel.dk>, <linux-block@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <shikemeng@huaweicloud.com>,
	<linfeilong@huawei.com>, <liuzhiqiang@huawei.com>
Subject: Re: [PATCH 1/5] sbitmap: don't consume nr for inactive waitqueue to avoid lost wakeups
Date: Thu, 01 Dec 2022 10:32:36 -0300	[thread overview]
Message-ID: <87y1rrmeq3.fsf@suse.de> (raw)
In-Reply-To: <20221201045408.21908-2-shikemeng@huawei.com> (Kemeng Shi's message of "Thu, 1 Dec 2022 12:54:04 +0800")

Kemeng Shi <shikemeng@huawei.com> writes:

> If we decremented queue without waiters, we should not decremente freed
> bits number "nr", or all "nr" could be consumed in a empty queue and no
> wakeup will be called.
> Currently, for case "wait_cnt > 0", "nr" will not be decremented if we
> decremented queue without watiers and retry is returned to avoid lost
> wakeups. However for case "wait_cnt == 0", "nr" will be decremented
> unconditionally and maybe decremented to zero. Although retry is
> returned by active state of queue, it's not actually executed for "nr"
> is zero.
>

Hi Kemeng,

Fwiw, I sent a patch rewriting this algorithm which is now merged in
axboe/for-next.  It drops the per-waitqueue wait_cnt entirely.  You can
find it here:

https://lore.kernel.org/lkml/20221110153533.go5qs3psm75h27mx@quack3/T/

Thanks!


-- 
Gabriel Krisman Bertazi

  parent reply	other threads:[~2022-12-01 13:32 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-01  4:54 [PATCH 0/5] A few cleanup and bugfix patches for sbitmap Kemeng Shi
2022-12-01  4:54 ` [PATCH 1/5] sbitmap: don't consume nr for inactive waitqueue to avoid lost wakeups Kemeng Shi
2022-12-01  7:21   ` Kemeng Shi
2022-12-02  0:58     ` Jens Axboe
2022-12-02  2:34       ` Kemeng Shi
2022-12-01 13:32   ` Gabriel Krisman Bertazi [this message]
2022-12-02  0:57     ` Kemeng Shi
2022-12-01  4:54 ` [PATCH 2/5] sbitmap: remove unnecessary calculation of alloc_hint in __sbitmap_get_shallow Kemeng Shi
2022-12-01  4:54 ` [PATCH 3/5] sbitmap: remove redundant check in __sbitmap_queue_get_batch Kemeng Shi
2022-12-01  4:54 ` [PATCH 4/5] sbitmap: rewrite sbitmap_find_bit_in_index to reduce repeat code Kemeng Shi
2022-12-01  4:54 ` [PATCH 5/5] sbitmap: add sbitmap_find_bit to remove repeat code in __sbitmap_get/__sbitmap_get_shallow Kemeng Shi

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