linux-kernel - RE: debugctl msr

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Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E08F10CB1@irsmsx504.ger.corp.intel.com>
Date:	Wed, 19 Nov 2008 15:47:39 +0000
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	"eranian@...il.com" <eranian@...il.com>
CC:	Markus Metzger <markus.t.metzger@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: debugctl msr

>-----Original Message-----
>From: stephane eranian [mailto:eranian@...glemail.com] 
>Sent: Mittwoch, 19. November 2008 14:00
>To: Metzger, Markus T
>Cc: Markus Metzger; Ingo Molnar; Andi Kleen; Andrew Morton; 
>linux-kernel@...r.kernel.org
>Subject: Re: debugctl msr
>

>I had to hack ds.c some more to make forward progress with PEBS. First
>of all my PEBS code is
>in a kernel module, so all PEBS functions have to be exported.
>Furhtermore, I need a
>ds_get_pebs_thres() and ds_set_pebs_thres() calls.

I'm having a deja vu. We had this discussion before. You reported those
issues and I fixed them. Same for the PEBS size; and Andi Kleen asked
to exclude ds.c from the build instead of guarding the .c file and to
use the mm semaphore in ds_allocate_buffer().

That thread ended in the multiplexing discussion and my fixes never got in.
I'll send a patch covering those problems next week.

Regarding access to the interrupt threshold, we never completed
our discussion.
If we look towards multiplexing, ds.c has to handle interrupts and
copy the trace to the various users - at least for BTS.
I will pull some of the BTS handling from ptrace into ds.c - ds.c needs
to be able to disable BTS recording for overflow handling and we would
not want this knowledge in two different places.

I would add those functions now to proceed with the perfmon2 adaptation
and later remove them again and put overflow handling into ds.c

I'll send a separate patch for those.

>But the one key problem is ds_validate_access(). I had to disable this
>function.

I agree that this is too ptrace centric.

It works fine for the ptrace bts extenstion since ptrace has similar
restrictions, already.

A better choice would be to return an opaque handle.

regards,
markus.
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