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Date: Mon, 29 Aug 2016 09:00:59 +0800
From: Yuyang Du <yuyang.du@intel.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Benjamin Segall <bsegall@google.com>, Paul Turner <pjt@google.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Mike Galbraith <umgwanakikbuti@gmail.com>
Subject: Re: [PATCH v1 07/10] sched/fair: Remove useless 64-bit to 32-bit
 variable conversion
Message-ID: <20160829010059.GG3273@intel.com>
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On Thu, Aug 25, 2016 at 09:11:56AM +0200, Vincent Guittot wrote:
> On 10 August 2016 at 02:14, Yuyang Du <yuyang.du@intel.com> wrote:
> > In __decay_sum(), the 64-bit to 32-bit variable conversion makes no
> > performance nor correctness use.
> 
> Are you sure that there is no impact on 32bits system ?
> Even this will be mainly shift manipulation
> 
 
Honestly, I didn't consider 32-bit system at all, :(

And after all, it's 64-bit shift 32-bit vs. 64-bit shift 64-bit operations.
I'm not an expert, but I intend to believe they are about the same, because
the arithmetic overhead seems to lie in the left part of the shift operation,
both of which are 64-bit (correct me if I'm wrong).