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From: Feng Tang <feng.tang@intel.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org,
	john.stultz@linaro.org, sboyd@kernel.org, corbet@lwn.net,
	Mark.Rutland@arm.com, maz@kernel.org, kernel-team@fb.com,
	neeraju@codeaurora.org, ak@linux.intel.com,
	zhengjun.xing@intel.com,
	Xing Zhengjun <zhengjun.xing@linux.intel.com>
Subject: Re: [PATCH v14 clocksource 4/6] clocksource: Reduce clocksource-skew threshold for TSC
Date: Wed, 12 May 2021 21:18:15 +0800	[thread overview]
Message-ID: <20210512131815.GA37641@shbuild999.sh.intel.com> (raw)
In-Reply-To: <20210512035156.GT975577@paulmck-ThinkPad-P17-Gen-1>

Hi Paul,

On Tue, May 11, 2021 at 08:51:56PM -0700, Paul E. McKenney wrote:
> On Wed, May 12, 2021 at 10:18:49AM +0800, Feng Tang wrote:
> > Hi Paul,
> > 
> > On Tue, May 11, 2021 at 04:34:53PM -0700, Paul E. McKenney wrote:

[SNIP]
> > >  	 * Ensure clocksources that have large 'mult' values don't overflow
> > >  	 * when adjusted.
> > > diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
> > > index a492e4da69ba..b3f608c2b936 100644
> > > --- a/kernel/time/jiffies.c
> > > +++ b/kernel/time/jiffies.c
> > > @@ -49,13 +49,14 @@ static u64 jiffies_read(struct clocksource *cs)
> > >   * for "tick-less" systems.
> > >   */
> > >  static struct clocksource clocksource_jiffies = {
> > > -	.name		= "jiffies",
> > > -	.rating		= 1, /* lowest valid rating*/
> > > -	.read		= jiffies_read,
> > > -	.mask		= CLOCKSOURCE_MASK(32),
> > > -	.mult		= TICK_NSEC << JIFFIES_SHIFT, /* details above */
> > > -	.shift		= JIFFIES_SHIFT,
> > > -	.max_cycles	= 10,
> > > +	.name			= "jiffies",
> > > +	.rating			= 1, /* lowest valid rating*/
> > > +	.uncertainty_margin	= TICK_NSEC,
> > 
> > 'jiffies' is known to be very bad as a watchdog ("worse bandaid" in
> > Thomas' words :)), and TICK_NSEC just turns to 1ms for HZ=1000 case. 
> > Maybe we should give it a bigger margin, like the 32ms margin for 
> > 'tsc-early'?
> > 
> > Other than this, it looks good to me, thanks!
> 
> As in the fixup diff below?

Yep, thanks,

> 
> Would you be willing to provide an ack or tested-by for the rest
> of the series?  (I have your ack on 1/6.)

I haven't figured out a way to check 5/6 patch yet, but feel free
to add my ack for the first 4 patches (1/6 ~ 4/6) 

	Acked-by: Feng Tang <feng.tang@intel.com>

Thanks,
Feng

> 
> 						Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
> index b3f608c2b936..01935aafdb46 100644
> --- a/kernel/time/jiffies.c
> +++ b/kernel/time/jiffies.c
> @@ -51,7 +51,7 @@ static u64 jiffies_read(struct clocksource *cs)
>  static struct clocksource clocksource_jiffies = {
>  	.name			= "jiffies",
>  	.rating			= 1, /* lowest valid rating*/
> -	.uncertainty_margin	= TICK_NSEC,
> +	.uncertainty_margin	= 32 * NSEC_PER_MSEC,
>  	.read			= jiffies_read,
>  	.mask			= CLOCKSOURCE_MASK(32),
>  	.mult			= TICK_NSEC << JIFFIES_SHIFT, /* details above */

  reply	other threads:[~2021-05-12 13:18 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-11 23:34 [PATCH v14 clocksource 0/5] Do not mark clocks unstable due to delays for v5.14 Paul E. McKenney
2021-05-11 23:34 ` [PATCH v14 clocksource 1/6] clocksource: Retry clock read if long delays detected Paul E. McKenney
2021-05-11 23:34 ` [PATCH v14 clocksource 2/6] clocksource: Check per-CPU clock synchronization when marked unstable Paul E. McKenney
2021-05-11 23:34 ` [PATCH v14 clocksource 3/6] clocksource: Limit number of CPUs checked for clock synchronization Paul E. McKenney
2021-05-11 23:34 ` [PATCH v14 clocksource 4/6] clocksource: Reduce clocksource-skew threshold for TSC Paul E. McKenney
2021-05-12  2:18   ` Feng Tang
2021-05-12  3:51     ` Paul E. McKenney
2021-05-12 13:18       ` Feng Tang [this message]
2021-05-12 17:14         ` Paul E. McKenney
2021-05-11 23:34 ` [PATCH v14 clocksource 5/6] clocksource: Provide kernel module to test clocksource watchdog Paul E. McKenney
2021-05-13  3:29   ` Feng Tang
2021-05-13  4:01     ` Paul E. McKenney
2021-05-11 23:34 ` [PATCH v14 clocksource 6/6] clocksource: Print deviation in nanoseconds for unstable case Paul E. McKenney
2021-05-12  2:21   ` Feng Tang
2021-05-12  3:38     ` Paul E. McKenney

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