linux-kernel - Re: [PATCH v2 3/3] sched: increase SCHED_LOAD

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Date:	Wed, 18 May 2011 12:39:55 -0700
From:	Nikhil Rao <ncrao@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Stephan Barwolf <stephan.baerwolf@...ilmenau.de>
Subject: Re: [PATCH v2 3/3] sched: increase SCHED_LOAD_SCALE resolution

On Wed, May 18, 2011 at 11:25 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Nikhil Rao <ncrao@...gle.com> wrote:
>
>> -#define SCHED_LOAD_SHIFT     10
>> +#if BITS_PER_LONG > 32
>> +#define SCHED_LOAD_RESOLUTION        10
>> +#define scale_load(w)                (w << SCHED_LOAD_RESOLUTION)
>> +#define scale_load_down(w)   (w >> SCHED_LOAD_RESOLUTION)
>> +#else
>> +#define SCHED_LOAD_RESOLUTION        0
>> +#define scale_load(w)                w
>> +#define scale_load_down(w)   w
>> +#endif
>
> Please use the:
>
> #if X
> # define Y A
> #else
> # define Y B
> #endif
>
> type of nested CPP branching style.
>
> Also, the 'w' probably wants to be '(w)', just in case.

Thanks for the review. Will fix the macros.

>
>>       if (!lw->inv_weight) {
>> -             if (BITS_PER_LONG > 32 && unlikely(lw->weight >= WMULT_CONST))
>> +             unsigned long w = scale_load_down(lw->weight);
>> +             if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
>>                       lw->inv_weight = 1;
>
> Please separate local variable declarations and the first statement following
> it by an extra empty line.
>

Yes, will do.

> Could you also put all the performance measurement description into the
> changelog of this third commit - so that people can see (and enjoy) the
> extensive testing you have done on this topic?
>

Yes, will add the performance changes to the commit description.

>>  /*
>> - * Increase resolution of nice-level calculations:
>> + * Increase resolution of nice-level calculations for 64-bit architectures.
>>   */
>> -#define SCHED_LOAD_SHIFT     10
>> +#if BITS_PER_LONG > 32
>> +#define SCHED_LOAD_RESOLUTION        10
>> +#define scale_load(w)                (w << SCHED_LOAD_RESOLUTION)
>> +#define scale_load_down(w)   (w >> SCHED_LOAD_RESOLUTION)
>> +#else
>> +#define SCHED_LOAD_RESOLUTION        0
>> +#define scale_load(w)                w
>> +#define scale_load_down(w)   w
>> +#endif
>
> Please also be a bit more verbose in the comment above why we treat 64-bit
> architectures differently - it's not obvious.

Added a more descriptive comment.


Thanks for the review. I'll refresh the patch and send it with the fixes.

-Thanks,
Nikhil
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