linux-kernel - Re: HW breakpoints perf

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Message-ID: <20100118110406.GC5256@nowhere>
Date:	Mon, 18 Jan 2010 12:04:07 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Joshua Pincus <joshua.pincus@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>, peterz@...radead.org,
	paulus@...ba.org, acme@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: HW breakpoints perf_events request

On Thu, Jan 14, 2010 at 10:03:27AM -0800, Joshua Pincus wrote:
> Hi,
> 
> On Thu, Jan 14, 2010 at 1:23 AM, Andi Kleen <andi@...stfloor.org> wrote:
> >> We would like to avoid using ptrace at all costs.
> >> It requires us to have a parent thread running
> >> which monitors all the others.  It's not clear that
> >> the wait() call by the parent doesn't mask a barrage
> >> of signals from various threads and the performance
> >
> > mask? It'll report them. You expect to have so
> > many signals that this would be a problem?
> 
> Yes.  We expect to see a zillion of them.

I don't quite understand what signals are masked here,
actually I'm not sure what is the true problem with ptrace.
Is it because a breakpoint in a thread is going to stop
all thread in the process until the parent handles the
signal?

Anyway, although I first suggested extending perf, with
more thoughts I now agree that perf should keep doing what
it does currently (profiling) and not trying to become an
messy mix of a profiler, debugger, etc...
This is not its role.

But it can certainly be used by a debugging facility.

What about extending ptrace to support a new type of
breakpoint debugging interface?

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