linux-kernel - Re: [RFC PATCH 1/1] smp: Change function signatures to use call_single_data

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Message-ID: <20230906140947.GA33104@noisy.programming.kicks-ass.net>
Date:   Wed, 6 Sep 2023 16:09:47 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Leonardo Bras <leobras@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Guo Ren <guoren@...nel.org>,
        Valentin Schneider <vschneid@...hat.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Yury Norov <yury.norov@...il.com>,
        Imran Khan <imran.f.khan@...cle.com>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] smp: Change function signatures to use
 call_single_data_t

On Thu, Aug 31, 2023 at 03:31:28AM -0300, Leonardo Bras wrote:
> call_single_data_t is a size-aligned typedef of struct __call_single_data.
> 
> This alignment is desirable in order to have smp_call_function*() avoid
> bouncing an extra cacheline in case of an unaligned csd, given this
> would hurt performance.
> 
> Since the removal of struct request->csd in commit 660e802c76c8
> ("blk-mq: use percpu csd to remote complete instead of per-rq csd") there
> are no current users of smp_call_function*() with unaligned csd.
> 
> Change every 'struct __call_single_data' function parameter to
> 'call_single_data_t', so we have warnings if any new code tries to
> introduce an smp_call_function*() call with unaligned csd.
> 
> Signed-off-by: Leonardo Bras <leobras@...hat.com>

Fair enough, I'll go queue it somewhere.