Date: Mon, 28 Jul 2014 08:54:13 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: "Yan, Zheng" <zheng.z.yan@intel.com>, linux-kernel@vger.kernel.org,
        mingo@kernel.org, acme@infradead.org, eranian@google.com
Subject: Re: [PATCH v3 6/9] perf, x86: handle multiple records in PEBS buffer
Message-ID: <20140728065413.GJ6758@twins.programming.kicks-ass.net>
References: <1406016602-31845-1-git-send-email-zheng.z.yan@intel.com>
 <1406016602-31845-7-git-send-email-zheng.z.yan@intel.com>
 <20140725081033.GV3935@laptop>
 <20140725150445.GG18735@two.firstfloor.org>
 <20140725155332.GC6758@twins.programming.kicks-ass.net>
 <20140725164041.GH18735@two.firstfloor.org>
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On Fri, Jul 25, 2014 at 06:40:41PM +0200, Andi Kleen wrote:
> > Suppose two pebs events, one has exclude_kernel set. It overflows,
> > before entering the kernel, the other event generates PEBS records from
> > inside the kernel with both events marked in the overflow field.
> >=20
> > And only once we leave the kernel can the exclude_kernel event tick
> > again and trigger the assist, finalyl clearing the bit.
> >=20
> > If you were to report the records to both events, one would get a lot of
> > kernel info he was not entitled to.
>=20
> Ok that case can be filtered in software. Shouldn't be too difficult.
> Perhaps just using ip
>=20
> 	if (event->attr.exclude_kernel && pebs->ip >=3D __PAGE_OFFSET)
> 	    skip;
> 	if (event->attr.exclude_user && pebs->ip < __PAGE_OFFSET)
> 	    skip;
>=20
> This would also help with the existing skid.
>=20
> Any other concerns?

Yeah, why fuck about and do ugly hacks when you can actually do it
right? That way you're sure you've not forgotten anything.

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