Re: [PATCH v4 15/21] PM / devfreq: rockchip-dfi: Add perf support

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: linux-rockchip@lists.infradead.org,
	Mark Rutland <mark.rutland@arm.com>,
	Heiko Stuebner <heiko@sntech.de>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	MyungJoo Ham <myungjoo.ham@samsung.com>,
	Michael Riesch <michael.riesch@wolfvision.net>,
	kernel@pengutronix.de, Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 15/21] PM / devfreq: rockchip-dfi: Add perf support
Date: Wed, 10 May 2023 21:56:34 +0200	[thread overview]
Message-ID: <20230510195634.GH29365@pengutronix.de> (raw)
In-Reply-To: <71827018-8e29-2966-380b-66ddfdcd3668@arm.com>

On Tue, May 09, 2023 at 09:04:58PM +0100, Robin Murphy wrote:
> On 2023-05-05 12:38, Sascha Hauer wrote:
> > The DFI is a unit which is suitable for measuring DDR utilization, but
> > so far it could only be used as an event driver for the DDR frequency
> > scaling driver. This adds perf support to the DFI driver.
> > 
> > Usage with the 'perf' tool can look like:
> > 
> > perf stat -a -e rockchip_ddr/cycles/,\
> > 		rockchip_ddr/read-bytes/,\
> > 		rockchip_ddr/write-bytes/,\
> > 		rockchip_ddr/bytes/ sleep 1
> > 
> >   Performance counter stats for 'system wide':
> > 
> >          1582524826      rockchip_ddr/cycles/
> >             1802.25 MB   rockchip_ddr/read-bytes/
> >             1793.72 MB   rockchip_ddr/write-bytes/
> >             3595.90 MB   rockchip_ddr/bytes/
> > 
> >         1.014369709 seconds time elapsed
> > 
> > perf support has been tested on a RK3568 and a RK3399, the latter with
> > dual channel DDR.
> 
> Might it be useful to offer the option of monitoring each channel
> individually?

I gave it a quick try. For my normal testing workload the values are
spread quite homogeneously:

 Performance counter stats for 'system wide':

        1062183406      rockchip_ddr/cycles/
           1517.57 MB   rockchip_ddr/read-bytes0/
           1517.11 MB   rockchip_ddr/write-bytes0/
           1519.78 MB   rockchip_ddr/read-bytes1/
           1514.97 MB   rockchip_ddr/write-bytes1/
           1518.69 MB   rockchip_ddr/read-bytes2/
           1516.01 MB   rockchip_ddr/write-bytes2/
           1519.37 MB   rockchip_ddr/read-bytes3/
           1515.46 MB   rockchip_ddr/write-bytes3/
          12137.84 MB   rockchip_ddr/bytes/

       1.005686209 seconds time elapsed

I found one workload that looks strange though:

 Performance counter stats for 'system wide':

        1076756945      rockchip_ddr/cycles/
           2326.55 MB   rockchip_ddr/read-bytes0/
             30.60 MB   rockchip_ddr/write-bytes0/
              0.24 MB   rockchip_ddr/read-bytes1/
              0.09 MB   rockchip_ddr/write-bytes1/
              0.21 MB   rockchip_ddr/read-bytes2/
              0.09 MB   rockchip_ddr/write-bytes2/
              0.30 MB   rockchip_ddr/read-bytes3/
              0.10 MB   rockchip_ddr/write-bytes3/
           2357.87 MB   rockchip_ddr/bytes/

I am running this tool (likely not the exact version):
https://github.com/mturquette/memtest/blob/master/mtest.c

I don't know yet what this tool is doing, but it somehow manages
to use only a single channel.

We might take this as a sign that monitoring the individual channels can
indeed be useful.

I'll address your other comments in the next round.

Thanks for your input

Sascha

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