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

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Message-ID: <1fee0372-3a3b-5e09-38c3-ffb3523fe195@intel.com>
Date:   Tue, 11 Apr 2023 06:43:39 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     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,
        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>,
        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 4/11/23 04:35, Mark Rutland wrote:
> I agree it'd be nice to have performance figures, but I think those would only
> need to demonstrate a lack of a regression rather than a performance
> improvement, and I think it's fairly clear from eyeballing the generated
> instructions that a regression isn't likely.

Thanks for the additional context.

I totally agree that there's zero burden here to show a performance
increase.  If anyone can think of a quick way to do _some_ kind of
benchmark on the code being changed and just show that it's free of
brown paper bags, it would be appreciated.  Nothing crazy, just think of
one workload (synthetic or not) that will stress the paths being changed
and run it with and without these changes.  Make sure there are not
surprises.

I also agree that it's unlikely to be brown paper bag material.