linux-kernel - Re: [PATCH 2/2] clocksource: arm_arch_timer: set arch_mem_timer cpumask to cpu_possible

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Date:   Tue, 10 Jul 2018 00:09:11 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sudeep Holla <sudeep.holla@....com>
cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <marc.zyngier@....com>,
        Kevin Hilman <khilman@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 2/2] clocksource: arm_arch_timer: set arch_mem_timer
 cpumask to cpu_possible_mask

On Mon, 9 Jul 2018, Sudeep Holla wrote:

> Currently, arch_mem_timer cpumask is set to cpu_all_mask which should be
> fine. However, cpu_possible_mask is more accurate and if there are other
> clockevent source in the system which are set to cpu_possible_mask, then
> having cpu_all_mask may result in issue.
> 
> E.g. on a platform with arm,sp804 timer with rating 300 and
> cpu_possible_mask and this arch_mem_timer timer with rating 400 and
> cpu_all_mask, tick_check_preferred may choose both preferred as the
> cpumasks are not equal though they must be.
> 
> This issue was root caused incorrectly initially and a fix was merged as
> commit 1332a9055801 ("tick: Prefer a lower rating device only if it's CPU
> local device").

To avoid that in the future we really should fix the decision logic to mask
out the non possible CPUs from the supplied masks.

Thanks,

	tgkx