linux-kernel - Re: [patch V4 00/36] rseq: Optimize exit to user space

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4029c2d2-7a0c-4531-aa1e-b35be9098bb1@kernel.dk>
Date: Wed, 10 Sep 2025 07:55:36 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>
Cc: Michael Jeanson <mjeanson@...icios.com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Peter Zijlstra <peterz@...radead.org>, "Paul E. McKenney"
 <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson
 <seanjc@...gle.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>, x86@...nel.org,
 Arnd Bergmann <arnd@...db.de>, Heiko Carstens <hca@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Huacai Chen <chenhuacai@...nel.org>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [patch V4 00/36] rseq: Optimize exit to user space

On 9/8/25 3:31 PM, Thomas Gleixner wrote:
> For your convenience all of it is also available as a conglomerate from
> git:
> 
>     git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git rseq/perf

I used this branch for some quick testing. Since I last looked at the
rseq performance overhead, glibc must have improved a few things. FWIW,
box is running libc 2.41 at the moment. Test box is on debian unstable,
so gets frequent updates. In any case, for one of my usual kernel
overhead runs of checking running a basic IOPS based test, I see the
following on the stock (-rc5 + 6.18 targeted changes) kernel running
that test:

+    0.89%  io_uring  [kernel.kallsyms]  [k] __get_user_8
+    0.58%  io_uring  [kernel.kallsyms]  [k] __put_user_8
+    1.13%  io_uring  [kernel.kallsyms]  [k] __rseq_handle_notify_resume

which is about 2.6% of purely rseq related overhead. Pulling in the
above branch and running the exact same test, all of the above are gone
and perusing the profile has nothing jump out at me in terms of shifting
those cycles to other bookkeeping.

So yes, this work does make a very noticeable difference!

-- 
Jens Axboe