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

Ingo Molnar
2008-11-28T14:40:54Z

* Ron <ron@debian.org> wrote:

> On Wed, Nov 26, 2008 at 04:16:38PM +0100, Peter Zijlstra wrote:
> > 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..1ce2e53 100644
> --- a/kernel/sched_clock.c
> +++ b/kernel/sched_clock.c
> @@ -37,7 +37,8 @@
> */
> 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);
> }
>
> static __read_mostly int sched_clock_running;
>
>
> Signed-off-by: Ron Lee <ron@debian.org>

whitespace damage: all tabs are space.

please see Documentation/email-clients.txt for how to send patches.

Also, when you resend a patch, do it without quotes and by including the
fill commit log again - to make it easier to apply it. (and not forcing
me to cut&paste various emails - it's fundamentall error-prone)

Ingo