linux-kernel - Re: [PATCH 1/2 -tip] sched: Clean unused fields from struct rq

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Date:	Tue, 17 Mar 2009 21:33:19 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Luis Henriques <henrix@...o.pt>
CC:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 -tip] sched: Clean unused fields from struct rq

Luis Henriques wrote:
> On Wed, Mar 18, 2009 at 01:09:29AM +0100, Peter Zijlstra wrote:
>   
>> On Wed, 2009-03-18 at 00:03 +0000, Luis Henriques wrote:
>>     
>>> Since they are used on in statistics and are always set to zero, the following
>>> frields from struct rq have been removed: yld_exp_empty, yld_act_empty and
>>> yld_both_empty.
>>>
>>> Signed-off-by: Luis Henriques <henrix@...o.pt>
>>> ---
>>>       
>>> +++ b/kernel/sched_stats.h
>>> @@ -26,9 +26,8 @@ static int show_schedstat(struct seq_file *seq, void *v)
>>>  
>>>  		/* runqueue-specific stats */
>>>  		seq_printf(seq,
>>> -		    "cpu%d %u %u %u %u %u %u %u %u %u %llu %llu %lu",
>>> -		    cpu, rq->yld_both_empty,
>>> -		    rq->yld_act_empty, rq->yld_exp_empty, rq->yld_count,
>>> +		    "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->ttwu_count, rq->ttwu_local,
>>>  		    rq->rq_cpu_time,
>>>       
>> I think this bit is ABI, so you either have to bump the version number
>> or emit 0s, iirc gregory touched some of that last -- or at least wrote
>> userspace for it..
>>     
>
> Hmm... you're right.  I should have though about that.  Anyway, what is the
> the best approach here?
>
> I know that changes in ABI shall not break anything, but just increasing the
> version number will really solve the issue?  Will userspace care for this?
> On the other hand, just writting 0s does not sound interesting either...
>
>   
Hi Luis,
  My app does check the version number, so bumping it is probably the
best solution.   Be sure to keep me in the loop about whether this patch
gets merged and I will be sure to update it to handle the new version.

Regards,
-Greg






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