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

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Date:   Thu, 22 Jun 2017 10:56:40 -0500
From:   Kim Phillips <kim.phillips@....com>
To:     Will Deacon <will.deacon@....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 Wed, 21 Jun 2017 16:31:09 +0100
Will Deacon <will.deacon@....com> wrote:

> 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

4MiB.

> and what (if any) value you're passing as aux_watermark?

None passed, but it looks like 4KiB was used since the AUXTRACE size
was 4MiB - 4KiB.

I'm not seeing the issue with a simple bts-based version I'm
working on...yet.  We can revisit if I'm able to reproduce again; the
problem could have been on the userspace side.

Meanwhile, when using fvp-base.dtb, my model setup stops booting the
kernel after "smp: Bringing up secondary CPUs ...".  If I however take
the second SPE node from fvp-base.dts and add it to my working device
tree, I get this during the driver probe:

[    1.042063] arm_spe_pmu spe-pmu@0: probed for CPUs 0-7 [max_record_sz 64, align 1, features 0xf]
[    1.043582] arm_spe_pmu spe-pmu@1: probed for CPUs 0-7 [max_record_sz 64, align 1, features 0xf]
[    1.043631] genirq: Flags mismatch irq 6. 00004404 (arm_spe_pmu) vs. 00004404 (arm_spe_pmu)
[    1.043784] arm_spe_pmu: probe of spe-pmu@1 failed with error -16

spe-pmu@0 is useable, but doubt spe-pmu@1 is.  btw, that 16 is EBUSY
"Device or resource busy".

Kim