linux-kernel - Re: [PATCH v3] Added perf functionality to mmdc driver

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Message-ID: <20160830125420.GG1223@leverpostej>
Date:   Tue, 30 Aug 2016 13:54:20 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Shawn Guo <shawnguo@...nel.org>
Cc:     Zhi Li <lznuaa@...il.com>, Zhengyu Shen <zhengyu.shen@....com>,
        Frank Li <frank.li@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com
Subject: Re: [PATCH v3] Added perf functionality to mmdc driver

Hi,

On Tue, Aug 30, 2016 at 07:43:29PM +0800, Shawn Guo wrote:
> On Mon, Aug 29, 2016 at 11:06:44AM -0500, Zhi Li wrote:
> > On Wed, Aug 17, 2016 at 2:42 PM, Zhengyu Shen <zhengyu.shen@....com> wrote:
> > > MMDC is a multi-mode DDR controller that supports DDR3/DDR3L x16/x32/x64
> > > and LPDDR2 two channel x16/x32 memory types. MMDC is configurable, high
> > > performance, and optimized. MMDC is present on i.MX6 Quad and i.MX6
> > > QuadPlus devices, but this driver only supports i.MX6 Quad at the moment.
> > > MMDC provides registers for performance counters which read via this
> > > driver to help debug memory throughput and similar issues.
> > >
> > > $ perf stat -a -e mmdc/busy-cycles/,mmdc/read-accesses/,mmdc/read-bytes/,mmdc/total-cycles/,mmdc/write-accesses/,mmdc/write-bytes/ dd if=/dev/zero of=/dev/null bs=1M count=5000
> > > Performance counter stats for 'dd if=/dev/zero of=/dev/null bs=1M count=5000':
> > >
> > >          898021787      mmdc/busy-cycles/
> > >           14819600      mmdc/read-accesses/
> > >             471.30 MB   mmdc/read-bytes/
> > >         2815419216      mmdc/total-cycles/
> > >           13367354      mmdc/write-accesses/
> > >             427.76 MB   mmdc/write-bytes/
> > >
> > >        5.334757334 seconds time elapsed
> > >
> > > Signed-off-by: Zhengyu Shen <zhengyu.shen@....com>
> > > Signed-off-by: Frank Li <frank.li@....com>
> > 
> > Shawn Guo:
> > 
> >          No new comments got more than 1 weeks.
> >          Did you plan accept it?
> 
> @Mark, how do you think of this version?

Sorry, I've been away for the last week and haven't had the chance to
look at this yet. I will try to get round to it in the next few days.

In the meantime, could you please try attacking this with Vince's perf
fuzzer [1] (as root, or with perf_event_paranoid dropped to -1)? It's
rather good at finding (subtle) issues in drivers.

Thanks,
Mark.

[1] https://github.com/deater/perf_event_tests