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From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Serge Semin <fancer.lancer@gmail.com>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Paul Burton <paulburton@kernel.org>,
	Ralf Baechle <ralf@linux-mips.org>,
	Alessandro Zummo <a.zummo@towertech.it>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Arnd Bergmann <arnd@arndb.de>, Rob Herring <robh+dt@kernel.org>,
	linux-mips@vger.kernel.org, linux-rtc@vger.kernel.org,
	devicetree@vger.kernel.org,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 7/7] clocksource: mips-gic-timer: Set limitations on clocksource/sched-clocks usage
Date: Mon, 18 May 2020 15:59:16 +0200	[thread overview]
Message-ID: <4c723219-62f8-be6a-47ea-a586859d832d@linaro.org> (raw)
In-Reply-To: <20200516121647.g6jua35kkihmw5r6@mobilestation>

On 16/05/2020 14:16, Serge Semin wrote:
> Hello Daniel,
> 
> Thanks for your comment. My response is below.
> 
> On Fri, May 15, 2020 at 07:10:04PM +0200, Daniel Lezcano wrote:
>> On Thu, May 07, 2020 at 12:41:07AM +0300, Serge Semin wrote:
>>> Currently neither clocksource nor scheduler clock kernel framework
>>> support the clocks with variable frequency. Needless to say how many
>>> problems may cause the sudden base clocks frequency change. In a
>>> simplest case the system time will either slow down or speed up.
>>> Since on CM2.5 and earlier MIPS GIC timer is synchronously clocked
>>> with CPU we must set some limitations on using it for these frameworks
>>> if CPU frequency may change. First of all it's not safe to have the
>>> MIPS GIC used for scheduler timings. So we shouldn't proceed with
>>> the clocks registration in the sched-subsystem. Secondly we must
>>> significantly decrease the MIPS GIC clocksource rating. This will let
>>> the system to use it only as a last resort.
>>>
>>> Note CM3.x-based systems may also experience the problems with MIPS GIC
>>> if the CPU-frequency change is activated for the whole CPU cluster
>>> instead of using the individual CPC core clocks divider.
>>
>> May be there is no alternative but the code looks a bit hacksih. Isn't possible
>> to do something with the sched_mark_unstable?
>>
>> Or just not use the timer at all ?
> 
> Not using the timer might be better, but not that good alternative either
> especially in our case due to very slow external timer. Me and Thomas
> Bogendoerfer discussed the similar commit I've provided to the csrc-r4k driver
> available on MIPS:
> https://lkml.org/lkml/2020/5/11/576
> 
> To cut it short, you are right. The solution with using clocksource_mark_unstable()
> is better alternative spied up in x86 tsc implementation. I'll use a similar
> approach here and submit the updated patch in v3.
> 
> Could you please proceed with the rest of the series review? I'd like to send
> the next version with as many comments taken into account as possible. The
> patchset has been submitted a while ago, but except Rob noone have had any
> comments.(

For me other patches are ok.

I can apply patches 1, 2, 4, 5, 6

Will remain patches 3 et 7


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  reply	other threads:[~2020-05-18 13:59 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200306125622.839ED80307C4@mail.baikalelectronics.ru>
2020-03-24 17:43 ` [PATCH v2 0/6] clocksource: Fix MIPS GIC and DW APB Timer for Baikal-T1 SoC support Sergey.Semin
2020-03-24 17:43   ` [PATCH v2 1/6] dt-bindings: rtc: Convert snps,dw-apb-timer to DT schema Sergey.Semin
2020-03-24 18:07     ` Alexandre Belloni
2020-03-24 18:20       ` Serge Semin
2020-03-31 20:14     ` Rob Herring
2020-03-24 17:43   ` [PATCH v2 2/6] dt-bindings: interrupt-controller: Convert mti,gic " Sergey.Semin
2020-03-31 21:02     ` Rob Herring
2020-04-01 10:19       ` Sergey Semin
2020-04-01 14:13         ` Rob Herring
2020-04-01 22:07           ` Sergey Semin
2020-05-06 21:41   ` [PATCH v3 0/7] clocksource: Fix MIPS GIC and DW APB Timer for Baikal-T1 SoC support Serge Semin
2020-05-06 21:41     ` [PATCH v3 1/7] dt-bindings: rtc: Convert snps,dw-apb-timer to DT schema Serge Semin
2020-05-06 21:41     ` [PATCH v3 2/7] dt-bindings: timer: Move snps,dw-apb-timer DT schema from rtc Serge Semin
2020-05-07 12:03       ` Alexandre Belloni
2020-05-14 19:04       ` Rob Herring
2020-05-06 21:41     ` [PATCH v3 3/7] dt-bindings: interrupt-controller: Convert mti,gic to DT schema Serge Semin
2020-05-14 19:06       ` Rob Herring
2020-05-18 14:51         ` Serge Semin
2020-05-06 21:41     ` [PATCH v3 4/7] clocksource: dw_apb_timer: Set clockevent any-possible-CPU mask Serge Semin
2020-05-06 21:41     ` [PATCH v3 5/7] clocksource: dw_apb_timer_of: Fix missing clockevent timers Serge Semin
2020-05-06 21:41     ` [PATCH v3 6/7] clocksource: mips-gic-timer: Register as sched_clock Serge Semin
2020-05-06 21:41     ` [PATCH v3 7/7] clocksource: mips-gic-timer: Set limitations on clocksource/sched-clocks usage Serge Semin
2020-05-15 17:10       ` Daniel Lezcano
2020-05-16 12:16         ` Serge Semin
2020-05-18 13:59           ` Daniel Lezcano [this message]
2020-05-18 14:40             ` Serge Semin
2020-05-18 14:45               ` Serge Semin

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