lkml.org 
[lkml]   [2012]   [May]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRE: [PATCH] sched: Make nr_uninterruptible count a signed value
The issue is because when promoting from 32-bit unsigned to 64-bit signed, the compiler first does SIZE increase and then the sign change. If it did SIGN change first and then size increase (with sign-extension) and it will work correctly.

But then, the compiler is probably doing the right thing here because the starting point is an unsigned value and when it is assigned a negative value, the compiler is perfectly justified in converting it to a large positive value which is what happened here.

The theoretical correct fix is to change the declaration to signed long nr_uninterruptible simply because it can sometimes become -ve.

The other fix is to fix the print statement - but it feels wrong.

It would be good to fix the declaration...

Thanks,
--Diwakar.

-----Original Message-----
From: Peter Zijlstra [mailto:peterz@infradead.org]
Sent: Wednesday, May 09, 2012 1:12 AM
To: Diwakar Tundlam
Cc: 'Ingo Molnar'; 'David Rientjes'; 'linux-kernel@vger.kernel.org'; Peter De Schrijver
Subject: RE: [PATCH] sched: Make nr_uninterruptible count a signed value
On Tue, 2012-05-08 at 15:46 -0700, Diwakar Tundlam wrote:
> 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.

Ah, quite possible. %Ld is indeed %lld and the value is long, not long long. So the proper fix is to fudge that printk statement somehow.

> Your machine is probably natively 64-bit.

Yeah, I gave up on 32bit computing a while ago..

\
 
 \ /
  Last update: 2012-05-09 21:41    [from the cache]
©2003-2011 Jasper Spaans