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

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Message-Id: <8b133053-247f-414b-9c01-e0e5291e347d@app.fastmail.com>
Date: Tue, 09 Jul 2024 09:47:52 +0800
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Daniel Lezcano" <daniel.lezcano@...aro.org>,
 "Aleksandar Rikalo" <aleksandar.rikalo@...mia.com>,
 "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>
Cc: "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



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.

Thanks
- Jiaxun

>
> Thanks
>
> -- 
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- Jiaxun