linux-kernel - Re: [PATCH 3/9] perf/x86: Add is_hardware

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Message-ID: <20150717161136.GH26091@leverpostej>
Date:	Fri, 17 Jul 2015 17:11:36 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"eranian@...gle.com" <eranian@...gle.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"Hunter, Adrian" <adrian.hunter@...el.com>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/9] perf/x86: Add is_hardware_event

On Fri, Jul 17, 2015 at 04:47:26PM +0100, Mark Rutland wrote:
> On Fri, Jul 17, 2015 at 04:03:36PM +0100, Liang, Kan wrote:
> > > 
> > > On Thu, Jul 16, 2015 at 09:33:45PM +0100, kan.liang@...el.com wrote:
> > > > From: Kan Liang <kan.liang@...el.com>
> > > >
> > > > Using is_hardware_event to replace !is_software_event to indicate a
> > > > hardware event.
> > > 
> > > Why...?
> > 
> > First, the comments of is_software_event is not correct. 
> > 0 or !is_software_event is not for a hardware event.
> > is_hardware_event is for a hardware event.
> 
> Circular logic is fantastic.

Sorry for the snark here. I completely misread this.

I agree that the comment is wrong. However, changing !is_software_event
to is_hardware_event is not always correct.

For example, perf_group_attach tests for the addition of a non-software
event to a software group, so we can mark the group as not consisting
solely of software events. For that to be done correctly, we need to
check !is_software_event.

I was wrong about the throttling, having confused active_oncpu and
nr_active. Sorry for the noise on that. However, as you mention that
does prevent the use of exclusive events for uncore PMUs, and I don't
see why that should change.

Thanks,
Mark.
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