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

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Message-ID: <bf4a45e9-4ed3-4d3b-bb96-add20a71b04c@linaro.org>
Date: Mon, 8 Jul 2024 18:36:07 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: 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>,
 Jiaxun Yang <jiaxun.yang@...goat.com>, linux-kernel@...r.kernel.org,
 linux-mips@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
 Paul Burton <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 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

Thanks

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