linux-kernel - Re: [patch 00/11] rseq: Optimize exit to user space

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Message-ID: <aa3b8329-59d1-4d6e-bccb-eb75a03762e9@efficios.com>
Date: Wed, 20 Aug 2025 10:27:22 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Thomas Gleixner <tglx@...utronix.de>, Jens Axboe <axboe@...nel.dk>,
 LKML <linux-kernel@...r.kernel.org>
Cc: Michael Jeanson <mjeanson@...icios.com>,
 Peter Zijlstra <peterz@...radead.org>, "Paul E. McKenney"
 <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 Wei Liu <wei.liu@...nel.org>
Subject: Re: [patch 00/11] rseq: Optimize exit to user space

On 2025-08-17 17:23, Thomas Gleixner wrote:
> On Thu, Aug 14 2025 at 00:08, Thomas Gleixner wrote:
>> On Wed, Aug 13 2025 at 15:36, Jens Axboe wrote:
>>> On 8/13/25 3:32 PM, Thomas Gleixner wrote:
>>>> Could you give it a test ride to see whether this makes a difference in
>>>> your environment?
>>>
>>> Yep, I'll give a spin.
>>
>> Appreciated.
> 
> Please do not use the git branch I had in the cover letter. I did some
> more analysis of this and it's even worse than I thought. Use
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git rseq/wip
> 
> instead.
> 
> I've rewritten the whole pile by now and made it a real fast path
> without the TIF_NOTIFY horror show, unless the fast path, which runs
> _after_ the TIF work loop faults. So far that happens once for each
> fork() as that has to fault in the copy of the user space rseq region.
> 

OK. I'll stop reviewing this version of the series and wait for an
updated version.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com