linux-kernel - Re: [PATCHv2 5/8] perf tools: Get precise

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Date:   Thu, 7 Mar 2019 23:32:46 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>,
        Nageswara R Sastry <nasastry@...ibm.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCHv2 5/8] perf tools: Get precise_ip from the pmu config

On Thu, Mar 07, 2019 at 08:51:23AM -0800, Andi Kleen wrote:
> On Thu, Mar 07, 2019 at 04:35:00PM +0100, Jiri Olsa wrote:
> > On Tue, Mar 05, 2019 at 08:40:17AM -0800, Andi Kleen wrote:
> > > On Tue, Mar 05, 2019 at 05:28:54PM +0100, Jiri Olsa wrote:
> > > > On Tue, Mar 05, 2019 at 08:13:19AM -0800, Andi Kleen wrote:
> > > > > On Tue, Mar 05, 2019 at 04:25:33PM +0100, Jiri Olsa wrote:
> > > > > > Getting precise_ip field from the perf_pmu::max_precise
> > > > > > config read from sysfs. If it's not available falling
> > > > > > back to current detection function.
> > > > > 
> > > > > max_precise depends on the event.  This won't work for all
> > > > > events. For example only instructions and cycles support
> > > > > ppp
> > > > 
> > > > I'm getting  precise_ip=3 on mem-* events as well, that's why I
> > > > was fixing this.. now it's not working for any event
> > > 
> > > I don't think it means anything for mem-*
> > > 
> > > There's some support for it on Goldmont plus for other events,
> > > but it doesn't support mem-*. On big core it's only
> > > for instructions and cycles, all implemented with the same
> > > event. All other PEBS events only have two levels
> > > switching between the two IPs.
> > 
> > ok, so how about this, it's the change I posted merged with the patch
> 
> Still seems like a hack. Even though I don't know of a case that
> would break now. But it would be better to have the precise probing
> in the open retry loop, instead of trying to reinvent it here.

right, I guess we could just set precise_ip hard to 3 for :P
and add fallback part for the precise_ip in perf_evsel__open

jirka