linux-kernel - Re: [PATCH] sched,fair: Remove > u32 weight handling for delta

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Message-ID: <20150706143920.GA2704@afzalpc>
Date:	Mon, 6 Jul 2015 20:09:20 +0530
From:	Afzal Mohammed <afzal.mohd.ma@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] sched,fair: Remove > u32 weight handling for delta

Hi,

On Mon, Jul 06, 2015 at 07:04:07PM +0530, Afzal Mohammed wrote:
> On Mon, Jul 06, 2015 at 01:44:30PM +0200, Peter Zijlstra wrote:
> > On Mon, Jul 06, 2015 at 08:14:37AM +0530, Afzal Mohammed wrote:

> > > The hunk being removed here
> > > would not make a difference to it as this is on scaled weight > u32.
> > > And pre-"9dbdb15553239" doesn't seem to have logical equivalent of hunk
> > > removed here either.
> > 
> > -ENOPARSE.
> 
> Reading 9dbdb15553239 ("sched/fair: Rework sched_fair time
> accounting") again, realized that I am wrong on this, that was
> referring to the below statement removed in that commit,
> 
>         if (likely(weight > (1UL << SCHED_LOAD_RESOLUTION)))
>                 tmp = (u64)delta_exec * scale_load_down(weight);
> 
> earlier came to a reasoning that as scale_load_down(weight) was not
> separately typecasted, value above u32 would be discarded, that non
> parsable statement meant that weight > u32 was not considered. Since
> cast has precedence over multiply, that statement of mine was wrong.

I take that back, consider as though I have not mentioned anything
above :)

Regards
Afzal
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