From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Michael Neuling <mikey@neuling.org>
Cc: Ingo Molnar <mingo@kernel.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
K Prasad <prasad@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org
Subject: Re: powerpc/perf: hw breakpoints return ENOSPC
Date: Thu, 16 Aug 2012 09:40:12 +0200 [thread overview]
Message-ID: <1345102812.31459.114.camel@twins> (raw)
In-Reply-To: <28857.1345091034@neuling.org>
On Thu, 2012-08-16 at 14:23 +1000, Michael Neuling wrote:
>=20
> 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=3D1), so we
> return ENOSPC.
I think this comes from the ptrace legacy, we register a breakpoint on
all cpus because when we migrate a task it cannot fail to migrate the
breakpoint.
Its one of the things I hate most about the hwbp stuff as it relates to
perf.
Frederic knows more...
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Michael Neuling <mikey@neuling.org>
Cc: K Prasad <prasad@linux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
Ingo Molnar <mingo@kernel.org>
Subject: Re: powerpc/perf: hw breakpoints return ENOSPC
Date: Thu, 16 Aug 2012 09:40:12 +0200 [thread overview]
Message-ID: <1345102812.31459.114.camel@twins> (raw)
In-Reply-To: <28857.1345091034@neuling.org>
On Thu, 2012-08-16 at 14:23 +1000, Michael Neuling wrote:
>
> 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.
I think this comes from the ptrace legacy, we register a breakpoint on
all cpus because when we migrate a task it cannot fail to migrate the
breakpoint.
Its one of the things I hate most about the hwbp stuff as it relates to
perf.
Frederic knows more...
next prev parent reply other threads:[~2012-08-16 7:40 UTC|newest]
Thread overview: 26+ 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 4:23 ` Michael Neuling
2012-08-16 7:40 ` Peter Zijlstra [this message]
2012-08-16 7:40 ` Peter Zijlstra
2012-08-16 11:17 ` Michael Neuling
2012-08-16 11:17 ` Michael Neuling
2012-08-16 11:44 ` Peter Zijlstra
2012-08-16 11:44 ` Peter Zijlstra
2012-08-16 14:02 ` Michael Ellerman
2012-08-16 14:02 ` Michael Ellerman
2012-08-16 14:15 ` Peter Zijlstra
2012-08-16 14:15 ` Peter Zijlstra
2012-08-17 1:20 ` Michael Ellerman
2012-08-17 1:20 ` Michael Ellerman
2012-08-16 23:34 ` Michael Neuling
2012-08-16 23:34 ` Michael Neuling
2012-08-17 16:15 ` Frederic Weisbecker
2012-08-17 16:15 ` Frederic Weisbecker
2012-08-17 21:58 ` Michael Neuling
2012-08-17 21:58 ` Michael Neuling
2012-09-25 7:10 ` Michael Neuling
2012-09-25 7:10 ` Michael Neuling
2012-09-27 15:23 ` Frederic Weisbecker
2012-09-27 15:23 ` Frederic Weisbecker
2012-09-27 1:02 ` Jovi Zhang
2012-09-27 1:02 ` Jovi Zhang
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