From: "Paul E. McKenney" <paulmck@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: 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, Chris Mason <clm@fb.com>
Subject: Re: [PATCH v8 clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog
Date: Fri, 16 Apr 2021 15:38:48 -0700 [thread overview]
Message-ID: <20210416223848.GL4212@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <878s5iuh10.ffs@nanos.tec.linutronix.de>
On Fri, Apr 16, 2021 at 10:10:51PM +0200, Thomas Gleixner wrote:
> On Tue, Apr 13 2021 at 21:35, Paul E. McKenney wrote:
> >
> > +static int inject_delay_freq;
> > +module_param(inject_delay_freq, int, 0644);
> > +static int inject_delay_run = 1;
> > +module_param(inject_delay_run, int, 0644);
>
> int? Can't we just make them 'unsigned int'? Negative values are not
> that useful.
>
> > +static int max_read_retries = 3;
> > +module_param(max_read_retries, int, 0644);
>
> max_read_retries is unused here. Should be in the patch which actually
> uses it.
Good point, I will make all three unsigned int and move max_read_retries
to 2/5 ("clocksource: Retry clock read if long delays detected").
> > +static void clocksource_watchdog_inject_delay(void)
> > +{
> > + int i;
> > + static int injectfail = -1;
> > +
> > + if (inject_delay_freq <= 0 || inject_delay_run <= 0)
> > + return;
> > + if (injectfail < 0 || injectfail > INT_MAX / 2)
> > + injectfail = inject_delay_run;
> > + if (!(++injectfail / inject_delay_run % inject_delay_freq)) {
>
> Operator precedence based cleverness is really easy to parse - NOT!
>
> > + pr_warn("%s(): Injecting delay.\n", __func__);
> > + for (i = 0; i < 2 * WATCHDOG_THRESHOLD / NSEC_PER_MSEC; i++)
> > + udelay(1000);
> > + pr_warn("%s(): Done injecting delay.\n", __func__);
> > + }
> > +
> > + WARN_ON_ONCE(injectfail < 0);
> > +}
>
> Brain melt stage reached by now.
>
> static unsigned int invocations, injections;
>
> if (!inject_delay_period || !inject_delay_repeat)
> return;
>
> if (!(invocations % inject_delay_period)) {
> mdelay(2 * WATCHDOG_THRESHOLD / NSEC_PER_MSEC);
> if (++injections < inject_delay_repeat)
> return;
> injections = 0;
> }
>
> invocations++;
> }
>
> Hmm?
That is quite a bit nicer than the interacting parameters that I
had. I will rework along these lines.
Thanx, Paul
next prev parent reply other threads:[~2021-04-16 22:38 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-14 4:34 [PATCH v8 clocksource] Do not mark clocks unstable due to delays for v5.13 Paul E. McKenney
2021-04-14 4:35 ` [PATCH v8 clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog Paul E. McKenney
2021-04-16 20:10 ` Thomas Gleixner
2021-04-16 22:38 ` Paul E. McKenney [this message]
2021-04-14 4:35 ` [PATCH v8 clocksource 2/5] clocksource: Retry clock read if long delays detected Paul E. McKenney
2021-04-16 20:45 ` Thomas Gleixner
2021-04-17 0:25 ` Paul E. McKenney
2021-04-17 12:24 ` Thomas Gleixner
2021-04-17 22:54 ` Paul E. McKenney
2021-04-17 23:15 ` Thomas Gleixner
2021-04-17 23:40 ` Paul E. McKenney
2021-04-14 4:36 ` [PATCH v8 clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable Paul E. McKenney
2021-04-17 12:28 ` Thomas Gleixner
2021-04-17 23:42 ` Paul E. McKenney
2021-04-17 12:47 ` Thomas Gleixner
2021-04-17 23:51 ` Paul E. McKenney
2021-04-18 16:20 ` Paul E. McKenney
2021-04-14 4:36 ` [PATCH v8 clocksource 4/5] clocksource: Provide a module parameter to fuzz per-CPU clock checking Paul E. McKenney
2021-04-14 4:36 ` [PATCH v8 clocksource 5/5] clocksource: Limit number of CPUs checked for clock synchronization Paul E. McKenney
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