From: Michael Neuling <mikey@neuling.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: K Prasad <prasad@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: powerpc/perf: hw breakpoints return ENOSPC
Date: Tue, 25 Sep 2012 17:10:14 +1000 [thread overview]
Message-ID: <29084.1348557014@neuling.org> (raw)
In-Reply-To: <11821.1345240695@neuling.org>
Michael Neuling <mikey@neuling.org> wrote:
> Frederic Weisbecker <fweisbec@gmail.com> wrote:
>
> > On Thu, Aug 16, 2012 at 02:23:54PM +1000, Michael Neuling wrote:
> > > Hi,
> > >
> > > I've been trying to get hardware breakpoints with perf to work on POWER7
> > > but I'm getting the following:
> > >
> > > % perf record -e mem:0x10000000 true
> > >
> > > Error: sys_perf_event_open() syscall returned with 28 (No space left on device). /bin/dmesg may provide additional information.
> > >
> > > Fatal: No CONFIG_PERF_EVENTS=y kernel support configured?
> > >
> > > true: Terminated
> > >
> > > (FWIW adding -a and it works fine)
> > >
> > > Debugging it seems that __reserve_bp_slot() is returning ENOSPC because
> > > it thinks there are no free breakpoint slots on this CPU.
> > >
> > > I have a 2 CPUs, so perf userspace is doing two perf_event_open syscalls
> > > to add a counter to each CPU [1]. The first syscall succeeds but the
> > > second is failing.
> > >
> > > On this second syscall, fetch_bp_busy_slots() sets slots.pinned to be 1,
> > > despite there being no breakpoint on this CPU. This is because the call
> > > the task_bp_pinned, checks all CPUs, rather than just the current CPU.
> > > POWER7 only has one hardware breakpoint per CPU (ie. HBP_NUM=1), so we
> > > return ENOSPC.
> > >
> > > The following patch fixes this by checking the associated CPU for each
> > > breakpoint in task_bp_pinned. I'm not familiar with this code, so it's
> > > provided as a reference to the above issue.
> > >
> > > Mikey
> > >
> > > 1. not sure why it doesn't just do one syscall and specify all CPUs, but
> > > that's another issue. Using two syscalls should work.
> >
> > This patch seems to make sense. I'll try it and run some tests.
> > Can I have your Signed-off-by ?
Frederic,
Did you ever get to testing or integrating this patch?
Mikey
> Of course...
>
> Signed-off-by: Michael Neuling <mikey@neuling.org>
next prev parent reply other threads:[~2012-09-25 7:10 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-16 4:23 powerpc/perf: hw breakpoints return ENOSPC Michael Neuling
2012-08-16 7:40 ` Peter Zijlstra
2012-08-16 11:17 ` Michael Neuling
2012-08-16 11:44 ` Peter Zijlstra
2012-08-16 14:02 ` Michael Ellerman
2012-08-16 14:15 ` Peter Zijlstra
2012-08-17 1:20 ` Michael Ellerman
2012-08-16 23:34 ` Michael Neuling
2012-08-17 16:15 ` Frederic Weisbecker
2012-08-17 21:58 ` Michael Neuling
2012-09-25 7:10 ` Michael Neuling [this message]
2012-09-27 15:23 ` Frederic Weisbecker
2012-09-27 1:02 ` Jovi Zhang
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