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From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
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 17:45:52 +0300	[thread overview]
Message-ID: <20200518144552.bjlddhuospgmer4j@mobilestation> (raw)
In-Reply-To: <20200518144045.v56fajrhbnnrzbpf@mobilestation>

On Mon, May 18, 2020 at 05:40:46PM +0300, Serge Semin wrote:
> Daniel,
> 
> On Mon, May 18, 2020 at 03:59:16PM +0200, Daniel Lezcano wrote:
> > 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
> 
> That's be great! Thanks. Is patch 3 supposed to be merged in by Rob or by you?
> I don't see one being in the Rob's repo. He might be waiting for you
> acknowledgment or something.

Ah, it's about the MIPS GIC IRQchip bindings conversion. No questions tabout
patch 3then. I'll ask Thomas about that patch status.

-Sergey 

> 
> I'll send the updated patch 3 shortly today.
> 
> -Sergey
> 
> > 
> > 
> > -- 
> > <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
> > 
> > Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
> > <http://twitter.com/#!/linaroorg> Twitter |
> > <http://www.linaro.org/linaro-blog/> Blog

      reply	other threads:[~2020-05-18 14:45 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
2020-05-18 14:40             ` Serge Semin
2020-05-18 14:45               ` Serge Semin [this message]

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