linux-kernel - Re: [linux-sunxi] [PATCH 0/8] clocksource: sunxi: Timer fixes and cleanup

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Message-ID: <51CC0BC3.5090309@redhat.com>
Date:	Thu, 27 Jun 2013 11:54:11 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
CC:	linux-sunxi@...glegroups.com, John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Emilio Lopez <emilio@...pez.com.ar>, kevin@...winnertech.com,
	sunny@...winnertech.com, shuge@...winnertech.com
Subject: Re: [linux-sunxi] [PATCH 0/8] clocksource: sunxi: Timer fixes and
 cleanup

Hi,

On 06/27/2013 11:43 AM, Maxime Ripard wrote:
> On Thu, Jun 27, 2013 at 11:27:02AM +0200, Hans de Goede wrote:
>> Hi,
>>
>> On 06/26/2013 11:16 PM, Maxime Ripard wrote:
>>> Hi everyone,
>>>
>>
>> <snip>
>>
>>> It also finally adds a clocksource from the free running counter found in the
>>> A10/A13 SoCs.
>>
>> Hmm, have you benchmarked this? There have been reports from linux-sunxi kernel
>> users (xbmc project) that the waiting for the latch is quite slow. Note we
>> don't have anything better yet in the linux-sunxi kernel.
>
> No. I didn't.
>
> Do you have any pointers to these discussions?
>

The original discussion should be somewhere here:
https://groups.google.com/forum/#!forum/linux-sunxi

But I could not find it (it is probably hidden under
an unlogical subject).

Looking at my own notes (a small TODO file), I've
written down that the reporter reports:

  -current clocksource can cause us to run with interrupts disabled for 17%
   of the time, see "perf top" output

This is with a workload which does a lot of gettimeofday
calls.

I notice that unlike the sunxi-3.4 code you don't do any locking,
so how do you stop 2 clocksource calls from racing (and thus
getting a possible wrong value because of things not
being properly latched) ?

Regards,

Hans
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