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Date:   Mon, 25 Apr 2022 11:35:09 +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 05/11] smp: replace smp_call_function_single_async()
 with  smp_call_private()
Message-ID: <20220425093509.GG2731@worktop.programming.kicks-ass.net>
References: <20220422200040.93813-1-dqiao@redhat.com>
 <20220422200040.93813-6-dqiao@redhat.com>
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On Fri, Apr 22, 2022 at 04:00:34PM -0400, Donghai Qiao wrote:
> Replaced smp_call_function_single_async() with smp_call_private()
> and also extended smp_call_private() to support one CPU synchronous
> call with preallocated csd structures.
> 
> Ideally, the new interface smp_call() should be able to do what
> smp_call_function_single_async() does. Because the csd is provided
> and maintained by the callers, it exposes the risk of corrupting
> the call_single_queue[cpu] linked list if the clents menipulate
> their csd inappropriately. On the other hand, there should have no
> noticeable performance advantage to provide preallocated csd for
> cross call kernel consumers. Thus, in the long run, the consumers
> should change to not use this type of preallocated csd.

You're completely missing the point of this interface. *please* look at
it more carefully.