Re: [RFC PATCH] sched: wakeup buddy

[Michael Wang]

Hi, Mike

Thanks for your reply.

On 02/28/2013 03:18 PM, Mike Galbraith wrote:
> On Thu, 2013-02-28 at 14:38 +0800, Michael Wang wrote:
> 
>> +				/*
>> +				 * current is the only task on rq and it is
>> +				 * going to sleep, current cpu will be a nice
>> +				 * candidate for p to run on.
>> +				 */
> 
> The sync hint only means it might be going to sleep soon, and even then,
> there can still be enough execution overlap to be a win to schedule
> cross core.  Sched pipe numbers will always be much prettier if you do
> wakeup cpu affine, as it's ~100% scheduler and ~100% sync.

Hmm.. so it's the comparison between 'cache benefit - execution overlap'
and 'latency - execution overlap'?

I could not estimate how many latency will be added to wait for current
going to sleep (it should be faster than access cold data, isn't it?),
but I really like the cache benefit, unless sync doesn't means current
is going to sleep every time, but that's the promise of WF_SYNC, isn't it?

You may lose
> a lot on other stuff if you interpret the hint as gospel truth.

Could you please give more details on this point?

> 
> IMHO, sched pipe is a "how fat have I become" benchmark, not "how well
> do I perform".  The scheduler performs well when it makes more work
> happen.  Playing ping-pong with yourself is _exercise_, not a job :)

That's right, may be I'm using the wrong description, it's the ops/sec
which has been doubled, that means 'fat', correct?

Regards,
Michael Wang

> 
> -Mike
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/