linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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 15:57:44 +0000	[thread overview]
Message-ID: <20200214155744.GA8784@arm.com> (raw)
In-Reply-To: <20200214154525.GA21875@arm.com>

On Friday 14 Feb 2020 at 15:45:25 (+0000), Ionela Voinescu wrote:
> 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/

I've mistakenly referenced a bad link ^

It was supposed to be:

[1] https://lore.kernel.org/lkml/20200211184542.29585-7-ionela.voinescu@arm.com/

Thanks,
Ionela.

      reply	other threads:[~2020-02-14 15:58 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
2020-02-14 15:57       ` Ionela Voinescu [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200214155744.GA8784@arm.com \
    --to=ionela.voinescu@arm.com \
    --cc=catalin.marinas@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=lukasz.luba@arm.com \
    --cc=mark.rutland@arm.com \
    --cc=maz@kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=rjw@rjwysocki.net \
    --cc=sudeep.holla@arm.com \
    --cc=suzuki.poulose@arm.com \
    --cc=tglx@linutronix.de \
    --cc=valentin.schneider@arm.com \
    --cc=vincent.guittot@linaro.org \
    --cc=viresh.kumar@linaro.org \
    --cc=will@kernel.org \
    --subject='Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).