linux-kernel - Re: [PATCH v2 0/5] locking: Introduce local{,64}_try

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Message-ID: <7360ffd2-a5aa-1373-8309-93e71ff36cbb@intel.com>
Date:   Wed, 5 Apr 2023 09:37:04 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Uros Bizjak <ubizjak@...il.com>, linux-alpha@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-arch@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Richard Henderson <richard.henderson@...aro.org>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Jun Yi <yijun@...ngson.cn>
Subject: Re: [PATCH v2 0/5] locking: Introduce local{,64}_try_cmpxchg

On 4/5/23 07:17, Uros Bizjak wrote:
> Add generic and target specific support for local{,64}_try_cmpxchg
> and wire up support for all targets that use local_t infrastructure.

I feel like I'm missing some context.

What are the actual end user visible effects of this series?  Is there a
measurable decrease in perf overhead?  Why go to all this trouble for
perf?  Who else will use local_try_cmpxchg()?

I'm all for improving things, and perf is an important user.  But, if
the goal here is improving performance, it would be nice to see at least
a stab at quantifying the performance delta.