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

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Date:	Thu, 27 Jun 2013 20:13:56 +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 06:54 PM, Maxime Ripard wrote:
> On Thu, Jun 27, 2013 at 11:54:11AM +0200, Hans de Goede wrote:
>> 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).
>
> I searched a bit and it seems to be that discussion:
> https://groups.google.com/d/msg/linux-sunxi/gaTDngPT7Is/oeLtWb1N1wIJ
>
>> 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.
>
> Siarhei however notes that even higher-end SoCs like the exynos5 have
> similar performances with that regard. So I'm not sure we can do
> something about it, except what is suggested in the above mail, which
> looks rather unsafe.
>
> Anyway, like you said, we have no easy other solution, and we lacked
> such support until now.
>
> So why not merge this code for now, and try to optimise it later if we
> find it's needed.

That is fine with me, I just wanted to share that this has shown as
a bottleneck in some benchmarks in case anyone has a clever idea to
fix it ...

Regards,

Hans
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