RE: [PATCH] sched: Make nr_uninterruptible count a signed value

From: Diwakar Tundlam
Date: Wed May 09 2012 - 14:55:31 EST


>> - 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.

--Diwakar.

-----Original Message-----
From: Michael Wang [mailto:wangyun@xxxxxxxxxxxxxxxxxx]
Sent: Wednesday, May 09, 2012 12:49 AM
To: Diwakar Tundlam
Cc: 'Peter Zijlstra'; 'Ingo Molnar'; 'David Rientjes'; 'linux-kernel@xxxxxxxxxxxxxxx'; 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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