lkml.org 
[lkml]   [2009]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC] perf_counter: Don't swap contexts containing locked mutex

* Ingo Molnar <mingo@elte.hu> wrote:

>
> * Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Fri, 2009-05-29 at 10:13 +0200, Peter Zijlstra wrote:
> > > On Fri, 2009-05-29 at 10:06 +0200, Peter Zijlstra wrote:
> > >
> > > > static struct perf_counter_ctx *pin_ctx(struct perf_counter *counter, u64 *old_gen)
> > > > {
> > > > struct perf_counter_context *ctx;
> > > > unsigned long flags;
> > > >
> > > > rcu_read_lock();
> > > > retry:
> > > > ctx = rcu_dereference(counter->ctx);
> > > > spin_lock_irqsave(&ctx->lock, flags);
> > > > if (ctx != rcu_dereference(counter->ctx))
> > > > goto retry;
> > > >
> > > > *old_gen = ctx->generation;
> > > > ctx->generation = ~0ULL;
> > > > spin_unlock_irqrestore(&ctx->lock, flags);
> > > > rcu_read_unlock();
> > > >
> > > > return ctx;
> > > > }
> > > >
> > > > static void unpin_ctx(struct perf_counter_ctx *ctx, u64 old_gen)
> > > > {
> > > > unsigned long flags;
> > > >
> > > > spin_lock_irqsave(&ctx->lock, flags);
> > > > ctx->generation = old_gen;
> > > > spin_unlock_irqrestore(&ctx->lock, flags);
> > > > }
> > >
> > > OK, I think I got this wrong, counter->ctx isn't the problem.
> > > task->perf_counter_ctx is.
> > >
> > > Still would be nice to write it in the above form. I'll go over the code
> > > again to see who else might want it.
> >
> > OK, I went over the code, and your patch does indeed cover the few
> > spots we need. It was just my brain going haywire and auditing the
> > wrong pattern.
>
> ok - i'll try this with my 'perf stat make -j' workload that
> quickly locks up on a Nehalem. (bug introduced by the context
> switch optimizations)

nope, that still hangs the box.

try the latest Git repo (i tried 95110d7) and do this:

make clean
perf stat -- make -j

that locks up for me, very quickly, with permanently stuck tasks:

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME COMMAND
10748 mingo 20 0 0 0 0 R 100.4 0.0 0:06.44 chmod
10756 mingo 20 0 0 0 0 R 100.4 0.0 0:06.43 touch

looping in the remove-context retry loop.

Ingo


\
 
 \ /
  Last update: 2009-05-29 11:19    [W:0.052 / U:1.848 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site