From: Jens Axboe <axboe@kernel.dk>
To: wenyang.linux@foxmail.com,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Dylan Yudaken <dylany@fb.com>,
David Woodhouse <dwmw@amazon.co.uk>,
Paolo Bonzini <pbonzini@redhat.com>, Fu Wei <wefu@redhat.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] eventfd: support delayed wakeup for non-semaphore eventfd to reduce cpu utilization
Date: Mon, 17 Apr 2023 08:38:15 -0600 [thread overview]
Message-ID: <817984a2-570c-cb23-4121-0d75005ebd4d@kernel.dk> (raw)
In-Reply-To: <tencent_AF886EF226FD9F39D28FE4D9A94A95FA2605@qq.com>
On 4/16/23 5:31?AM, wenyang.linux@foxmail.com wrote:
> From: Wen Yang <wenyang.linux@foxmail.com>
>
> For the NON SEMAPHORE eventfd, if it's counter has a nonzero value,
> then a read(2) returns 8 bytes containing that value, and the counter's
> value is reset to zero. Therefore, in the NON SEMAPHORE scenario,
> N event_writes vs ONE event_read is possible.
>
> However, the current implementation wakes up the read thread immediately
> in eventfd_write so that the cpu utilization increases unnecessarily.
>
> By adding a configurable delay after eventfd_write, these unnecessary
> wakeup operations are avoided, thereby reducing cpu utilization.
What's the real world use case of this, and what would the expected
delay be there? With using a delayed work item for this, there's
certainly a pretty wide grey zone in terms of delay where this would
perform considerably worse than not doing any delayed wakeups at all.
--
Jens Axboe
next prev parent reply other threads:[~2023-04-17 14:38 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-16 11:31 [PATCH] eventfd: support delayed wakeup for non-semaphore eventfd to reduce cpu utilization wenyang.linux
2023-04-17 8:22 ` Bagas Sanjaya
2023-04-17 12:44 ` kernel test robot
2023-04-17 14:38 ` Jens Axboe [this message]
2023-04-17 16:32 ` Wen Yang
2023-04-19 2:15 ` Jens Axboe
2023-04-19 9:12 ` Christian Brauner
2023-04-19 15:23 ` Wen Yang
2023-04-19 16:42 ` Jens Axboe
2023-04-20 17:44 ` Wen Yang
2023-05-04 16:01 ` Wen Yang
[not found] <20230417000711.1100-1-hdanton@sina.com>
2023-04-18 14:12 ` Wen Yang
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