linux-kernel - RE: [PATCH] eventfd: convert to using ->write

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Message-ID: <de316af8f88947fabd1422b04df8a66e@AcuMS.aculab.com>
Date:   Mon, 3 May 2021 16:12:02 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jens Axboe' <axboe@...nel.dk>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] eventfd: convert to using ->write_iter()

From: Jens Axboe
> Sent: 03 May 2021 15:58
> 
> Had a report on writing to eventfd with io_uring is slower than it
> should be, and it's the usual case of if a file type doesn't support
> ->write_iter(), then io_uring cannot rely on IOCB_NOWAIT being honored
> alongside O_NONBLOCK for whether or not this is a non-blocking write
> attempt. That means io_uring will punt the operation to an io thread,
> which will slow us down unnecessarily.
> 
> Convert eventfd to using fops->write_iter() instead of fops->write().

Won't this have a measurable performance degradation on normal
code that does write(event_fd, &one, 4);

	David

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