From: Eric Biggers <ebiggers@kernel.org>
To: Christian Brauner <brauner@kernel.org>
Cc: chenzhiyin <zhiyin.chen@intel.com>,
viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, nanhai.zou@intel.com
Subject: Re: [PATCH] fs.h: Optimize file struct to prevent false sharing
Date: Tue, 30 May 2023 18:55:49 -0700 [thread overview]
Message-ID: <20230531015549.GA1648@quark.localdomain> (raw)
In-Reply-To: <20230530-wortbruch-extra-88399a74392e@brauner>
On Tue, May 30, 2023 at 10:50:42AM +0200, Christian Brauner wrote:
> On Mon, May 29, 2023 at 10:06:26PM -0400, chenzhiyin wrote:
> > In the syscall test of UnixBench, performance regression occurred
> > due to false sharing.
> >
> > The lock and atomic members, including file::f_lock, file::f_count
> > and file::f_pos_lock are highly contended and frequently updated
> > in the high-concurrency test scenarios. perf c2c indentified one
> > affected read access, file::f_op.
> > To prevent false sharing, the layout of file struct is changed as
> > following
> > (A) f_lock, f_count and f_pos_lock are put together to share the
> > same cache line.
> > (B) The read mostly members, including f_path, f_inode, f_op are
> > put into a separate cache line.
> > (C) f_mode is put together with f_count, since they are used
> > frequently at the same time.
> >
> > The optimization has been validated in the syscall test of
> > UnixBench. performance gain is 30~50%, when the number of parallel
> > jobs is 16.
> >
> > Signed-off-by: chenzhiyin <zhiyin.chen@intel.com>
> > ---
>
> Sounds interesting, but can we see the actual numbers, please?
> So struct file is marked with __randomize_layout which seems to make
> this whole reordering pointless or at least only useful if the
> structure randomization Kconfig is turned off. Is there any precedence
> to optimizing structures that are marked as randomizable?
Most people don't use CONFIG_RANDSTRUCT. So it's still worth optimizing struct
layouts for everyone else.
- Eric
next prev parent reply other threads:[~2023-05-31 1:55 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-30 2:06 [PATCH] fs.h: Optimize file struct to prevent false sharing chenzhiyin
2023-05-30 8:50 ` Christian Brauner
2023-05-30 10:02 ` Amir Goldstein
2023-05-31 11:15 ` Christian Brauner
2023-05-31 1:55 ` Eric Biggers [this message]
2023-05-31 7:54 ` Christian Brauner
2023-06-01 9:24 ` chenzhiyin
2023-06-01 9:49 ` Christian Brauner
2023-06-01 10:06 ` Bernd Schubert
2023-06-05 12:58 ` Christian Brauner
2023-05-31 10:31 ` Chen, Zhiyin
2023-05-31 22:30 ` Dave Chinner
2023-06-01 10:47 ` Chen, Zhiyin
2023-06-02 0:47 ` Dave Chinner
2023-06-02 11:01 ` Chen, Zhiyin
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