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

From: Yuyang Du
Date: Mon Aug 29 2016 - 04:55:52 EST

On Thu, Aug 25, 2016 at 09:11:56AM +0200, Vincent Guittot wrote:
> On 10 August 2016 at 02:14, Yuyang Du <yuyang.du@xxxxxxxxx> 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).