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DateSun, 11 Jul 2004 23:37:50 -0700
FromAndrew Morton <>
SubjectRe: [PATCH] Instrumenting high latency
Con Kolivas <kernel@kolivas.org> wrote:
>
> Because of the recent discussion about latency in the kernel I asked William
> Lee Irwin III to help create some instrumentation to determine where in the
> kernel there were still sustained periods of non-preemptible code. He hacked
> together this simple patch which times periods according to the preempt
> count.

Looks sane.

> The patch appears to require CONFIG_PREEMPT enabled on uniprocessor and is
> i386 only at the moment.

Not sure what you mean by "on uniprocessor"? AFAICT the patch will work
as-is on uniprocessor and on SMP. Looks like it'll work with
CONFIG_PREEMPT=n, too, although that would be a slightly bizarre thing to
do.

+ print_symbol("%s\n",
+ __get_cpu_var(preempt_exit));

I'll change this to

print_symbol("%s",
__get_cpu_var(preempt_exit));
printk("\n");

so it doesn't make a mess with CONFIG_KALLSYMS=n.

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