On Fri, 28 Sep 2007 20:48:59 +0200 Peter Zijlstra <[email protected]> wrote:
>
> On Fri, 2007-09-28 at 11:49 -0700, Andrew Morton wrote:
>
> > Do you know where the stalls are occurring? throttle_vm_writeout(), or via
> > direct calls to congestion_wait() from page_alloc.c and vmscan.c? (running
> > sysrq-w five or ten times will probably be enough to determine this)
>
> would it make sense to instrument congestion_wait() callsites with
> vmstats?
Better than nothing, but it isn't a great fit: we'd need one vmstat counter
per congestion_wait() callsite, and it's all rather specific to the
kernel-of-the-day.
taskstats delay accounting isn't useful either - it will aggregate all the
schedule() callsites.
profile=sleep is just about ideal for this, isn't it? I suspect that most
people don't know it's there, or forgot about it.
It could be that profile=sleep just tells us "you're spending a lot of time
in io_schedule()" or congestion_wait(), so perhaps we need to teach it to
go for walk up the stack somehow.
But lockdep knows how to do that already so perhaps we (ie: you ;)) can
bolt sleep instrumentation onto lockdep as we (ie you ;)) did with the
lockstat stuff?
(Searches for the lockstat documentation)
Did we forget to do that?
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