linux-kernel - Re: [PATCH v4 07/14] clocksource: mips-gic-timer: Always use cluster 0 counter as clocksource

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Message-ID: <4729a8ba-655d-4127-9f14-33b4521b4442@linaro.org>
Date: Tue, 9 Jul 2024 16:44:30 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 Jiaxun Yang <jiaxun.yang@...goat.com>
Cc: Aleksandar Rikalo <aleksandar.rikalo@...mia.com>,
 Aleksandar Rikalo <arikalo@...il.com>, Chao-ying Fu <cfu@...ecomp.com>,
 Geert Uytterhoeven <geert@...ux-m68k.org>, Greg Ungerer <gerg@...nel.org>,
 Hauke Mehrtens <hauke@...ke-m.de>,
 Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>, linux-kernel@...r.kernel.org,
 "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
 Marc Zyngier <maz@...nel.org>, "paulburton@...nel.org"
 <paulburton@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Serge Semin <fancer.lancer@...il.com>, Thomas Gleixner <tglx@...utronix.de>,
 Tiezhu Yang <yangtiezhu@...ngson.cn>
Subject: Re: [PATCH v4 07/14] clocksource: mips-gic-timer: Always use cluster
 0 counter as clocksource

On 09/07/2024 10:53, Thomas Bogendoerfer wrote:
> On Tue, Jul 09, 2024 at 09:47:52AM +0800, Jiaxun Yang wrote:
>>
>>
>> 在2024年7月9日七月 上午12:36，Daniel Lezcano写道：
>>> On 11/05/2024 12:43, Aleksandar Rikalo wrote:
>>>> From: Paul Burton <paulburton@...nel.org>
>>>>
>>>> In a multi-cluster MIPS system we have multiple GICs - one in each
>>>> cluster - each of which has its own independent counter. The counters in
>>>> each GIC are not synchronised in any way, so they can drift relative to
>>>> one another through the lifetime of the system. This is problematic for
>>>> a clocksource which ought to be global.
>>>>
>>>> Avoid problems by always accessing cluster 0's counter, using
>>>> cross-cluster register access. This adds overhead so we only do so on
>>>> systems where we actually have CPUs present in multiple clusters.
>>>> For now, be extra conservative and don't use gic counter for vdso or
>>>> sched_clock in this case.
>>>>
>>>> Signed-off-by: Paul Burton <paulburton@...nel.org>
>>>> Signed-off-by: Chao-ying Fu <cfu@...ecomp.com>
>>>> Signed-off-by: Dragan Mladjenovic <dragan.mladjenovic@...mia.com>
>>>> Signed-off-by: Aleksandar Rikalo <aleksandar.rikalo@...mia.com>
>>>> ---
>>>
>>> Applied patch 7 and 8
>>
>> I think it won't compile without patch 1 being applid.
>>
>> Thomas, do you mind to apply patch 1 for now? Given that it's just some extra
>> function definitions.
> 
> no problem, I've applied patch 1 und 2 to mips-next.

Usually we create a shared immutable branch, but as we are close to the 
PR, I propose I ack these two patches and let them go through the mips 
tree this time

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