linux-kernel - Re: [PATCH v3 0/5] Cavium ThunderX uncore PMU support

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Message-ID: <20161028151749.GG14402@arm.com>
Date:   Fri, 28 Oct 2016 16:17:49 +0100
From:   Will Deacon <will.deacon@....com>
To:     Jan Glauber <jan.glauber@...iumnetworks.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 0/5] Cavium ThunderX uncore PMU support

On Thu, Oct 20, 2016 at 01:23:51PM +0200, Jan Glauber wrote:
> On Thu, Oct 20, 2016 at 12:37:07PM +0200, Peter Zijlstra wrote:
> > On Thu, Oct 20, 2016 at 11:30:36AM +0200, Jan Glauber wrote:
> > > Note:
> > > I'm using perf_sw_context in difference to perf_invalid_context
> > > (see WARN_ON in perf_pmu_register). Reason is that with perf_invalid_context
> > > add() is never called and the counter results are shown as "unsupported" by
> > > perf. With perf_sw_context everything works as expected.
> > 
> > What?! All the uncore PMUs use perf_invalid_context. What doesn't work
> > for you?
> 
> OK, so using perf_invalid_context and "-a" seems to work.
> 
> But I must say that I hate that from a user perspective. The user needs to know about
> the type of PMU behind the event and then provide "-a" or get a "<not supported"
> as counter value?

Sure, but in the interest of getting *something* merged, can we start
off using perf_invalid_context and then have the discussion about whether
or not this can be extended later on, please? If your PMU is a shared
resource amongst CPUs, it maybe that all you want is a better error
message from the perf tool (but again, this can come later!).

Will