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SubjectRe: [PATCH] update: preemptive kernel for O(1) sched
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On January 14, 2002 05:34 am, Robert Love wrote:
> A version of preempt-stats for the 2.5 series kernel is available at:
>
> ftp://ftp.kernel.org/pub/linux/kernel/people/rml/preempt-stats
>
> and your favorite mirror. Patches for 2.4 are available, too.
>
> This patch, used on top of preempt-kernel, allows the measuring of
> periods of non-preemptible so that we can identify long-held locks. The
> patch creates a proc entry, latencytimes, which contains the top 20
> worst-case recorded periods since it was last read. To begin recording,
> read the file once. Subsequent reads will return the results. I.e.,

Nice, but you need a way to turn it off, for example:

echo >/proc/latencytimes

i.e., truncate.

> [23:25:08]rml@langston:~$ cat /proc/latencytimes
> Worst 20 latency times of 277 measured in this period.
> usec cause mask start line/file address end line/file
> 9982 spin_lock 0 488/sched.c c0117ee2 645/irq.c
> 968 BKL 0 666/tty_io.c c0193d58 645/irq.c
> 430 spin_lock 0 69/i387.c c010f34f 96/mmx.c
> 103 ide0 0 583/irq.c c010ab1c 645/irq.c
> 100 BKL 0 2562/buffer.c c014abda 2565/buffer.c
> 54 BKL 0 702/tty_io.c c019406b 704/tty_io.c
> ... etc

A more typical form for the file/line would be, e.g., irq.c:645

> The goal would be to identity the problem areas and fix them.

Yep, sorry about the nits but that's the way we nitbots are programmed.

--
Daniel

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