linux-kernel - Re: [PATCH v4 0/5] Add support for the ARMv8.2 Statistical Profiling Extension

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Date:   Wed, 21 Jun 2017 16:31:09 +0100
From:   Will Deacon <will.deacon@....com>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
        tglx@...utronix.de, peterz@...radead.org,
        alexander.shishkin@...ux.intel.com, robh@...nel.org,
        suzuki.poulose@....com, pawel.moll@....com,
        mathieu.poirier@...aro.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/5] Add support for the ARMv8.2 Statistical Profiling
 Extension

On Thu, Jun 15, 2017 at 10:57:35AM -0500, Kim Phillips wrote:
> On Mon, 12 Jun 2017 11:20:48 -0500
> Kim Phillips <kim.phillips@....com> wrote:
> 
> > On Mon, 12 Jun 2017 12:08:23 +0100
> > Mark Rutland <mark.rutland@....com> wrote:
> > 
> > > On Mon, Jun 05, 2017 at 04:22:52PM +0100, Will Deacon wrote:
> > > > This is the sixth posting of the patches previously posted here:
> ...
> > > Kim, do you have any version of the userspace side that we could look
> > > at?
> > > 
> > > For review, it would be really helpful to have something that can poke
> > > the PMU, even if it's incomplete or lacking polish.
> > 
> > Here's the latest push, based on a a couple of prior versions of this
> > driver:
> > 
> > http://linux-arm.org/git?p=linux-kp.git;a=shortlog;h=refs/heads/armspev0.1
> > 
> > I don't seem to be able to get any SPE data output after rebasing on
> > this version of the driver.  Still don't know why at the moment...
> 
> Bisected to commit e38ba76deef "perf tools: force uncore events to
> system wide monitoring".  So, using record with specifying a -C
> <cpu> explicitly now produces SPE data, but only a couple of valid
> records at the beginning of each buffer; the rest is filled with
> PADding (0's).
> 
> I see Mark's latest comments have found a possible issue in the perf
> aux buffer handling code in the driver, and that the driver does some
> memset of padding (0's) itself; could that be responsible for the above
> behaviour?

Possibly. Do you know how big you're mapping the aux buffer and what (if
any) value you're passing as aux_watermark?

Will