linux-kernel - Re: [PATCH v4 05/12] this_cpu_cmpxchg: x86: switch this_cpu_cmpxchg to locked, add

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Message-ID: <20230306112240.GB1267364@hirez.programming.kicks-ass.net>
Date:   Mon, 6 Mar 2023 12:22:40 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Aaron Tomlin <atomlin@...mlin.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Russell King <linux@...linux.org.uk>,
        Huacai Chen <chenhuacai@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>, x86@...nel.org
Subject: Re: [PATCH v4 05/12] this_cpu_cmpxchg: x86: switch this_cpu_cmpxchg
 to locked, add _local function

On Sun, Mar 05, 2023 at 10:37:02AM -0300, Marcelo Tosatti wrote:
> Goal is to have vmstat_shepherd to transfer from
> per-CPU counters to global counters remotely. For this,
> an atomic this_cpu_cmpxchg is necessary.
> 
> Following the kernel convention for cmpxchg/cmpxchg_local,
> change x86's this_cpu_cmpxchg_ helpers to be atomic.
> and add this_cpu_cmpxchg_local_ helpers which are not atomic.

Urgh.. much hate for this. this_cpu_*() is local, per definition,
always.