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Date:   Mon, 25 Apr 2022 11:33:17 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Donghai Qiao <dqiao@redhat.com>
Cc:     akpm@linux-foundation.org, sfr@canb.auug.org.au, arnd@arndb.de,
        heying24@huawei.com, andriy.shevchenko@linux.intel.com,
        axboe@kernel.dk, rdunlap@infradead.org, tglx@linutronix.de,
        gor@linux.ibm.com, donghai.w.qiao@gmail.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 04/11] smp: replace smp_call_function_single() with
 smp_call()
Message-ID: <20220425093317.GF2731@worktop.programming.kicks-ass.net>
References: <20220422200040.93813-1-dqiao@redhat.com>
 <20220422200040.93813-5-dqiao@redhat.com>
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On Fri, Apr 22, 2022 at 04:00:33PM -0400, Donghai Qiao wrote:
> Eliminated the percpu global csd_data and temporarily hook up
> to smp_call().
> 
> There is no obvious reason or evidence that the differentiation

Using the on-stack csd seems like an obvious benefit to me. Stack is
often cache-hot, while the percpu stuff is likely a cache-miss. Worse,
the call_function_data as used by the mask functions is likely a double
miss due to the O(n^2) nature of the thing.