linux-kernel - Re: [PATCH] sched: Update scheduler stat documentation.

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Date:	Tue, 17 Jan 2012 10:50:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: Update scheduler stat documentation.


* Rakib Mullick <rakib.mullick@...il.com> wrote:

> On Mon, Jan 16, 2012 at 2:36 PM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> >
> > Yes - but we should also change it to export a value of zero.
> > The field is a legacy 'array expirations' field, and as such it
> > should be zero.
> >
> 
> Ok, thanks for suggestions. Please, look at the following patch, it's
> been roughly created to address your suggestion. If it looks okay,
> then I can send formal patch (perhaps two separate patches?). In this
> way, I think we can also remove rq->sched_switch field (not done in
> this patch)?
> 
> diff --git a/Documentation/scheduler/sched-stats.txt
> b/Documentation/scheduler/sched-stats.txt
> index 1cd5d51..cc2d107 100644
> --- a/Documentation/scheduler/sched-stats.txt
> +++ b/Documentation/scheduler/sched-stats.txt
> @@ -38,7 +38,8 @@ First field is a sched_yield() statistic:
>       1) # of times sched_yield() was called
> 
>  Next three are schedule() statistics:
> -     2) # of times we switched to the expired queue and reused it
> +     2) This field is a legacy array expiration field used in O(1) scheduler.
> +	But still kept for ABI integrity.

I'd formulate it like this:

> +     2) This field is a legacy array expiration count field
> +        used in the O(1) scheduler. We kept it for ABI
> +        compatibility, but it is always set to zero.


> +		int rq_sched_switch = 0;
>  #ifdef CONFIG_SMP
>  		struct sched_domain *sd;
>  		int dcount = 0;
> @@ -34,7 +35,7 @@ static int show_schedstat(struct seq_file *seq, void *v)
>  		seq_printf(seq,
>  		    "cpu%d %u %u %u %u %u %u %llu %llu %lu",
>  		    cpu, rq->yld_count,
> -		    rq->sched_switch, rq->sched_count, rq->sched_goidle,
> +		    rq_sched_switch, rq->sched_count, rq->sched_goidle,

printf can print a 0 value just fine as part of the format 
string ... :-)

But yeah, this logic is what i had in mind.

Thanks,

	Ingo
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