linux-kernel - Re: [patch] fix for sched_clock() when using jiffies

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1227712598.4454.199.camel@twins>
Date:	Wed, 26 Nov 2008 16:16:38 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ron <ron@...ian.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [patch] fix for sched_clock() when using jiffies

On Thu, 2008-11-27 at 01:36 +1030, Ron wrote:
> Hi,
> 
> I'm in the process of updating a port for an ARM based chip we've been
> working on, from 2.6.22-rc4'ish to the current HEAD of Linus' tree, and
> I started seeing the following:
> 
> [    0.000000] PID hash table entries: 512 (order: 9, 2048 bytes)
> [42949372.970000] Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
> 
> The reason appears to be that printk_clock() has been replaced with a
> call to cpu_clock, which in our case currently falls back to the default
> (weak) implementation of sched_clock() that uses jiffies -- but doesn't
> account for the initial offset of the jiffy count.  The following simple
> patch fixes it for me, in line with what printk_clock used to do.
> 

Looks good, except I suspect this line will now be longer than 80
characters and you forgot to provide your signed-off-by line.

> 
> diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
> index 8178724..d76814e 100644
> --- a/kernel/sched_clock.c
> +++ b/kernel/sched_clock.c
> @@ -37,7 +37,7 @@
>   */
>  unsigned long long __attribute__((weak)) sched_clock(void)
>  {
> -       return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
> +       return (unsigned long long)(jiffies - INITIAL_JIFFIES) * (NSEC_PER_SEC / HZ);
>  }
>  
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/