Re: [PATCH v1 07/10] sched/fair: Remove useless 64-bit to 32-bit variable conversion

From	Yuyang Du <yuyang.du@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v1 07/10] sched/fair: Remove useless 64-bit to 32-bit variable conversion
Date	2016-08-29 11:00 +0200
Message-ID	<sbqA9-56r-25@gated-at.bofh.it> (permalink)
References	<s4GA2-f8-9@gated-at.bofh.it> <s4HPs-16w-13@gated-at.bofh.it> <s9X7c-6ey-19@gated-at.bofh.it>
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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).

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Re: [PATCH v1 07/10] sched/fair: Remove useless 64-bit to 32-bit  variable conversion Yuyang Du <yuyang.du@intel.com> - 2016-08-29 11:00 +0200

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