linux-kernel - Re: [PATCH] sched: Make nr_uninterruptible count a signed value

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Date:	Thu, 10 May 2012 12:46:16 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Diwakar Tundlam <dtundlam@...dia.com>
CC:	"'Peter Zijlstra'" <peterz@...radead.org>,
	"'Ingo Molnar'" <mingo@...nel.org>,
	"'David Rientjes'" <rientjes@...gle.com>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>
Subject: Re: [PATCH] sched: Make nr_uninterruptible count a signed value

On 05/10/2012 02:55 AM, Diwakar Tundlam wrote:

>>> -       P(nr_uninterruptible);
>>> +       P((signed long)nr_uninterruptible);
> 
> I thought of it too, but it won't compile because the P macro expands to dereferencing rq->nr_uninterruptible, so with your change, it will show up as rq->(signed long)nr_uninterruptible which is a syntax error.
> 

oh, I see, so looks like it's a little hard to avoid some ugly change...

--Michael Wang

> --Diwakar.
> 
> -----Original Message-----
> From: Michael Wang [mailto:wangyun@...ux.vnet.ibm.com] 
> Sent: Wednesday, May 09, 2012 12:49 AM
> To: Diwakar Tundlam
> Cc: 'Peter Zijlstra'; 'Ingo Molnar'; 'David Rientjes'; 'linux-kernel@...r.kernel.org'; Peter De Schrijver
> Subject: Re: [PATCH] sched: Make nr_uninterruptible count a signed value
> 
> On 05/09/2012 06:46 AM, Diwakar Tundlam wrote:
> 
>>> No that's right. nr_uninterruptible counts the number of tasks in 
>>> uninterruptible sleep, so deactivate_task puts a task to sleep, so we 
>>> need to increment the number of sleeping tasks, activate_task wakes a 
>>> task up so we need to decrement the number of sleeping tasks.
>>
>> Yep, I looked at the code for task_contributes_to_load() and I understand what it is all about.
>> The ++ and -- are correct, I see it now.
>>
>> On the -ve values, strangely inspite of %Ld in the print statement, in my kernel, I see high unsigned values instead of -ve values for nr_uninterruptible.
>>
>> But the sum is always 0, though.
>>
>> Maybe it is an artifact of 32-bit machine displaying 64-bit print format.
>> An (unsigned long)(-24) promoted to (signed long long) ends up as 4294967272.
>> As seen in my output of sched_debug.
> 
> 
> This may do some help.
> 
> Regards,
> Michael Wang
> ---
>  kernel/sched/debug.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index 09acaa1..ab9d53f 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -270,7 +270,7 @@ static void print_cpu(struct seq_file *m, int cpu)
>                    rq->load.weight);
>         P(nr_switches);
>         P(nr_load_updates);
> -       P(nr_uninterruptible);
> +       P((signed long)nr_uninterruptible);
>         PN(next_balance);
>         P(curr->pid);
>         PN(clock);
> --
> 1.7.4.1
> 


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