linux-kernel - Re: [RESEND PATCH 2/2] locking/x86: Wire up sync_try

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Date:   Fri, 29 Sep 2023 07:45:51 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RESEND PATCH 2/2] locking/x86: Wire up sync_try_cmpxchg

On Thu, Sep 28, 2023 at 10:53 PM Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * Uros Bizjak <ubizjak@...il.com> wrote:
>
> > Implement target specific support for sync_try_cmpxchg.
>
> Could you please provide a before/after description of how
> this improves things exactly?

The improvement [1] was demonstrated in the original patch submission.
The resent part of the patch series is an infrastructure part, which
introduces a new locking primitive, together with its fallback, so it
has to be committed first. The improvement is in the other part of the
kernel, and this part requires the infrastructure part.

To avoid unwanted patch dependencies, I propose to commit the
infrastructure part first, and after that commit the XEN part of the
series. (Please note that the XEN part is already acked by the
maintainer). I will mention the concrete improvement (code
simplification as shown in [1] and better generated assembly for x86
targets) in the formal submission of the XEN part.

Please also note checksums in include/linux/atomic header files. It is
necessary to regenerate the headers every time the checksum changes.
The resend of the infrastructure part was thus necessary due to the
recent fixes in this area.

[1] https://lore.kernel.org/lkml/20230710192440.47140-3-ubizjak@gmail.com/

Thanks,
Uros.