From: Ionela Voinescu <ionela.voinescu@arm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com,
maz@kernel.org, suzuki.poulose@arm.com, sudeep.holla@arm.com,
lukasz.luba@arm.com, valentin.schneider@arm.com,
rjw@rjwysocki.net, peterz@infradead.org, mingo@redhat.com,
vincent.guittot@linaro.org, viresh.kumar@linaro.org,
linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate
Date: Fri, 14 Feb 2020 15:45:25 +0000 [thread overview]
Message-ID: <20200214154525.GA21875@arm.com> (raw)
In-Reply-To: <87mu9mgg41.fsf@nanos.tec.linutronix.de>
Hi Thomas,
On Friday 14 Feb 2020 at 01:35:58 (+0100), Thomas Gleixner wrote:
> Ionela Voinescu <ionela.voinescu@arm.com> writes:
>
> > From: Valentin Schneider <valentin.schneider@arm.com>
> >
> > Using an arch timer with a frequency of less than 1MHz can result in an
> > incorrect functionality of the system which assumes a reasonable rate.
> >
> > One example is the use of activity monitors for frequency invariance
> > which uses the rate of the arch timer as the known rate of the constant
> > cycle counter in computing its ratio compared to the maximum frequency
> > of a CPU. For arch timer frequencies less than 1MHz this ratio could
> > end up being 0 which is an invalid value for its use.
> >
> > Therefore, warn if the arch timer rate is below 1MHz which contravenes
> > the recommended architecture interval of 1 to 50MHz.
> >
> > Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
>
> So this patch is from Valentin. Where is his Signed-off-by?
>
Yes, sorry about this. This was based on a diff that Valentin provided
in v2. I'll change the author as agreed at:
https://lore.kernel.org/lkml/20200212103249.GA19041@arm.com/
> >
> > +static int validate_timer_rate(void)
> > +{
> > + if (!arch_timer_rate)
> > + return -EINVAL;
> > +
> > + /* Arch timer frequency < 1MHz can cause trouble */
> > + WARN_ON(arch_timer_rate < 1000000);
>
> This does not make sense to me. If the rate is out of bounds then why
> warn an just continue instead of making it fail?
>
Because it's not a hard restriction, it's just atypical for the rate to
be below 1Mhz. The spec only mentions a typical range of 1 to 50MHz and
the warning is only here to flag a potentially problematic rate, below
what is assumed typical in the spec.
In [1], where I'm actually relying on arch_timer_rate being higher than
than 1/SCHED_CAPACITY_SCALE² of the maximum frequency, I am making it
fail, as, for that scenario, it is a hard restriction.
+ * We use a factor of 2 * SCHED_CAPACITY_SHIFT -> SCHED_CAPACITY_SCALE²
+ * in order to ensure a good resolution for arch_max_freq_scale for
+ * very low arch timer frequencies (up to the KHz range which should be
+ * unlikely).
+ */
+ ratio = (u64)arch_timer_get_rate() << (2 * SCHED_CAPACITY_SHIFT);
+ ratio = div64_u64(ratio, max_freq_hz);
+ if (!ratio) {
+ pr_err("System timer frequency too low.\n");
+ return -EINVAL;
+ }
+
[1] https://lore.kernel.org/lkml/89339501-5ee4-e871-3076-c8b02c6fbf6e@arm.com/
Thanks,
Ionela.
> Thanks,
>
> tglx
next prev parent reply other threads:[~2020-02-14 15:45 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 18:45 [PATCH v3 0/7] arm64: ARMv8.4 Activity Monitors support Ionela Voinescu
2020-02-11 18:45 ` [PATCH v3 1/7] arm64: add support for the AMU extension v1 Ionela Voinescu
2020-02-12 11:30 ` Suzuki Kuruppassery Poulose
2020-02-12 14:54 ` Valentin Schneider
2020-02-12 16:10 ` Ionela Voinescu
2020-02-12 16:20 ` Suzuki Kuruppassery Poulose
2020-02-12 18:20 ` Ionela Voinescu
2020-02-12 19:24 ` Suzuki K Poulose
2020-02-12 20:19 ` Ionela Voinescu
2020-02-12 16:24 ` Vladimir Murzin
2020-02-12 18:27 ` Ionela Voinescu
2020-02-11 18:45 ` [PATCH v3 2/7] arm64: trap to EL1 accesses to AMU counters from EL0 Ionela Voinescu
2020-02-12 11:44 ` Suzuki Kuruppassery Poulose
2020-02-12 15:36 ` Valentin Schneider
2020-02-11 18:45 ` [PATCH v3 3/7] arm64/kvm: disable access to AMU registers from kvm guests Ionela Voinescu
2020-02-12 15:36 ` Valentin Schneider
2020-02-12 16:33 ` Suzuki Kuruppassery Poulose
2020-02-11 18:45 ` [PATCH v3 4/7] Documentation: arm64: document support for the AMU extension Ionela Voinescu
2020-02-12 15:36 ` Valentin Schneider
2020-02-11 18:45 ` [PATCH v3 5/7] cpufreq: add function to get the hardware max frequency Ionela Voinescu
2020-02-12 4:14 ` Viresh Kumar
2020-02-13 11:59 ` Valentin Schneider
2020-02-13 12:59 ` Ionela Voinescu
2020-02-13 15:22 ` Valentin Schneider
2020-02-11 18:45 ` [PATCH v3 6/7] arm64: use activity monitors for frequency invariance Ionela Voinescu
2020-02-12 18:59 ` Lukasz Luba
2020-02-13 9:47 ` Ionela Voinescu
2020-02-17 16:59 ` Valentin Schneider
2020-02-23 18:49 ` Ionela Voinescu
2020-02-11 18:45 ` [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate Ionela Voinescu
2020-02-12 9:30 ` Valentin Schneider
2020-02-12 10:32 ` Ionela Voinescu
2020-02-12 10:01 ` Lukasz Luba
2020-02-12 10:12 ` Marc Zyngier
2020-02-12 10:54 ` Ionela Voinescu
2020-02-12 10:55 ` Lukasz Luba
2020-02-12 11:10 ` Marc Zyngier
2020-02-12 11:43 ` Lukasz Luba
2020-02-12 11:12 ` Valentin Schneider
2020-02-14 0:35 ` Thomas Gleixner
2020-02-14 15:45 ` Ionela Voinescu [this message]
2020-02-14 15:57 ` Ionela Voinescu
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