linux-kernel - Re: [PATCH V1 Resend 2/5] tick-common: don't check tick_oneshot_mode_active() from tick_check

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Message-ID: <CAKohponxwG4ECBz21S7F0fjWs3LM7hFLBQBhPi60b+WS_P+x4Q@mail.gmail.com>
Date:	Wed, 16 Apr 2014 09:37:04 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Arvind Chauhan <Arvind.Chauhan@....com>,
	Linaro Networking <linaro-networking@...aro.org>
Subject: Re: [PATCH V1 Resend 2/5] tick-common: don't check
 tick_oneshot_mode_active() from tick_check_preferred()

On 16 April 2014 00:00, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Tue, 15 Apr 2014, Viresh Kumar wrote:
>
>> If 'curdev' passed to tick_check_preferred() is the current clock_event_device
>> then these two checks look exactly same, because td->mode is set to
>> TICKDEV_MODE_ONESHOT only when the event device has ONESHOT feature.
>>
>>       if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
>>               return false;
>>
>>       if (tick_oneshot_mode_active())
>>               return false;
>>
>> Now left the case where 'curdev' is not the current clock_event_device. This can
>> happen from the sequence started from clockevents_replace(). Here we are trying
>> to find the best possible device that we should choose. And so even in this case
>> we don't need the above check as we aren't really worried about the current
>> device.
>
> Wrong. If curdev is NULL, you might select a device w/o ONESHOT if the
> system is in oneshot mode. Go figure.

Okay, so the logs must have another case where curdev is NULL. But codewise
we are already taking care of that here:

        return !curdev ||
                newdev->rating > curdev->rating ||
               !cpumask_equal(curdev->cpumask, newdev->cpumask);

And so this patch wouldn't harm. And this is preserved in the next patch (3/5)
as well, which adds checks for other cases as well.
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