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

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Date:   Wed, 28 Jun 2017 20:16:38 -0500
From:   Kim Phillips <kim.phillips@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     <robh@...nel.org>, <mathieu.poirier@...aro.org>,
        <pawel.moll@....com>, <suzuki.poulose@....com>,
        <marc.zyngier@....com>, Will Deacon <will.deacon@....com>,
        <linux-kernel@...r.kernel.org>,
        <alexander.shishkin@...ux.intel.com>, <peterz@...radead.org>,
        <mingo@...hat.com>, <tglx@...utronix.de>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 0/5] Add support for the ARMv8.2 Statistical
 Profiling Extension

On Wed, 28 Jun 2017 12:32:50 +0100
Mark Rutland <mark.rutland@....com> wrote:

> On Wed, Jun 28, 2017 at 12:26:02PM +0100, Mark Rutland wrote:
> > On Tue, Jun 27, 2017 at 04:07:58PM -0500, Kim Phillips wrote:
> > > FWIW, there is also this one I saw with mmap-pages set to 5
> > > (pages), which gets rounded up to 8 pages:
> > 
> > Sorry, *what* does the rounding upwards? Userspace, perf core, or the
> > driver? Where?

SPE implementations may vary from the minimum buffer alignment of the
smallest available page size, so I left the bts userspace tool code's
upwards-rounding code intact for now.  

I'll take this opportunity to submit the SPE perf tool patch in the
form of a reply to this email:  Look for the rounding code in
tools/perf/arch/arm64/util/arm-spe.c:arm_spe_recording_options().

> > That's worrying. I'll see if I can reproduce this.
> 
> Actually, this might be down to the IDX2OFF() macro being borked for non
> power-of-two buffer sizes.
> 
> Do you have Will's latest fixes? In his tree there's a commit:
> 
>   4f331cd62531dce2 ("squash! drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension")
> 
> ... which should fix the IDX2OFF() bug.

yes, I've been running with that squash! commit since a couple of days
after I noticed it over a week ago.

> It's be good to reproduce the issue if we can, regardless.

FWIW, I couldn't the little I tried today.

Kim