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SubjectRe: [PATCH] i386 tsc: remove xtime_lock'ing around cpufreq notifier
On Wed, 11 Apr 2007 09:29:04 -0700
Daniel Walker <dwalker@mvista.com> wrote:

> The locking of the xtime_lock around the cpu notifier is unessesary now. At one
> time the tsc was used after a frequency change for timekeeping, but the re-write
> of timekeeping no longer uses the TSC unless the frequency is constant.
>
> The variables that are changed in this section of code had also once been used
> for timekeeping, but not any longer ..
>
> Signed-Off-By: Daniel Walker <dwalker@mvista.com>
>
> ---
> arch/i386/kernel/tsc.c | 8 +-------
> 1 file changed, 1 insertion(+), 7 deletions(-)
>
> Index: linux-2.6.20/arch/i386/kernel/tsc.c
> ===================================================================
> --- linux-2.6.20.orig/arch/i386/kernel/tsc.c
> +++ linux-2.6.20/arch/i386/kernel/tsc.c
> @@ -200,13 +200,10 @@ time_cpufreq_notifier(struct notifier_bl
> {
> struct cpufreq_freqs *freq = data;
>
> - if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
> - write_seqlock_irq(&xtime_lock);
> -
> if (!ref_freq) {
> if (!freq->old){
> ref_freq = freq->new;
> - goto end;
> + return 0;
> }
> ref_freq = freq->old;
> loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
> @@ -237,9 +234,6 @@ time_cpufreq_notifier(struct notifier_bl
> }
> }
> }
> -end:
> - if (val != CPUFREQ_RESUMECHANGE && val != CPUFREQ_SUSPENDCHANGE)
> - write_sequnlock_irq(&xtime_lock);
>
> return 0;
> }

hm.

I've been permadropping Andi's
ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt-current/patches/sched-clock-share
because it causes a lockup when initscripts start ondemand on my
single-CPU, CONFIG_SMP=n Vaio.

I don't know _why_ it locks up - I traced it down to the
write_seqlock_irq() which you have just removed. But write_seqlock()
doesn't loop with CONFIG_SMP=n builds, so a hang there is quite mysterious.

Anyway, your patch might make that hang go away. We'll see.
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