linux-kernel - Re: [PATCH] drivers/clocksource/arm_arch_timer: Tighten Allwinner arch timer workaround

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Date:   Thu, 10 Nov 2022 12:10:01 +0100
From:   Ilya Dikariev <dikarill@...u.de>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Samuel Holland <samuel@...lland.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Škrabec <jernej.skrabec@...il.com>,
        linux-sunxi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/clocksource/arm_arch_timer: Tighten Allwinner
 arch timer workaround

El Thu, 10 Nov 2022 08:31:21 +0000
Marc Zyngier <maz@...nel.org> escribió:

MZ> > 
MZ> > As we know, the Allwinner A64 SoC has a buggy RCU time unit. The  
MZ> 
MZ> What is RCU?

I think I called it wrong. Anyway I mean the HR timer of A64.

MZ> 
MZ> > workaround named UNKNOWN1 was not sufficient to cover some more buggy
MZ> > bunches of this SoC. This workaround diminish the mask to 8 bits instead
MZ> > of 9.
MZ> > 
MZ> > An example run of timer test tool https://github.com/smaeul/timer-tools
MZ> > on PinePhone device (owns the A64 SoC) gives following result on a non
MZ> > patched kernel (cut off):
MZ> > 
MZ> > Running parallel counter test...
MZ> > 0: Failed after 5507 reads (0.003578 s)
MZ> > 0: 0x0000000c8272cbf1 -> 0x0000000c8272ccff -> 0x0000000c8272cc0e (     0.011 ms)

[......]

MZ> > After the proposed patch applied the test runs
MZ> > correctly (~2 hours of testing with a tool above without fails)  
MZ> 
MZ> 2 hours seems like an incredibly small amount of time given that the
MZ> existing workaround was believed to be correct. Run it continuously
MZ> for a couple of weeks on several different machines with varying
MZ> workloads and less us know the outcome.

The only A64 machine I own is the Pinephone. First time I did this patch
~9 month ago (on behalf os Samuel). Before it the system suffered hangs
every 15-20 minutes and backward time jumps ~1 time a day.
Since applying of this patch none of above occurred.
To be honest, I never did long tests (weeks). I will put the device
on a probe for some weeks and let you know then.

Best regards,
Ilya

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