linux-kernel - Re: [PATCH v5 00/25] Add perf support to the rockchip-dfi driver

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Date:   Thu, 15 Jun 2023 15:27:15 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Sebastian Reichel <sebastian.reichel@...labora.com>
Cc:     linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, Heiko Stuebner <heiko@...ech.de>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>, kernel@...gutronix.de,
        Michael Riesch <michael.riesch@...fvision.net>,
        Robin Murphy <robin.murphy@....com>,
        Vincent Legoll <vincent.legoll@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH v5 00/25] Add perf support to the rockchip-dfi driver

On Wed, Jun 14, 2023 at 03:40:34PM +0200, Sebastian Reichel wrote:
> Hi,
> 
> On Wed, May 24, 2023 at 10:31:28AM +0200, Sascha Hauer wrote:
> > This is v5 of the series adding perf support to the rockchip DFI driver.
> > 
> > A lot has changed in the perf driver since v4. First of all the review
> > feedback from Robin and Jonathan has been integrated. The perf driver
> > now not only supports monitoring the total DDR utilization, but also the
> > individual channels. I also reworked the way the raw 32bit counter
> > values are summed up to 64bit perf values, so hopefully the code is
> > easier to follow now.
> > 
> > lockdep found out that that locking in the perf driver was broken, so I
> > reworked that as well. None of the perf hooks allows locking with
> > mutexes or spinlocks, so in perf it's not possible to enable the DFI
> > controller when needed. Instead I now unconditionally enable the DFI
> > controller during probe when perf is enabled.
> > 
> > Furthermore the hrtimer I use for reading out the hardware counter
> > values before they overflow race with perf. Now a seqlock is used to
> > prevent that.
> > 
> > The RK3588 device tree changes for the DFI were not part of v4. As
> > Vincent Legoll showed interest in testing this series the necessary
> > device tree changes are now part of this series.
> 
> I tested the series on RK3588 EVB1. The read/write byts looks
> sensible. Sometimes cycles reads unrealistic values, though:
> 
>  Performance counter stats for 'system wide':
> 
> 18446744070475110400      rockchip_ddr/cycles/

This goes down to missing initialization of &dfi->last_perf_count, see
my other mail. Will fix this in the next round.

Sascha

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