linux-kernel - Re: Not able to use HIGH_RES

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAB4K4y5ZkGY3pe3ty5fbaVTj626dAS3HuodX6HfDvym8g0qyZQ@mail.gmail.com>
Date:	Wed, 21 Mar 2012 15:46:39 +0530
From:	Ajeet Yadav <ajeet.yadav.77@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: Not able to use HIGH_RES_TIMERS on ARM

Hi John,
Thank for clearing the confusion.

On Wed, Mar 21, 2012 at 10:28 AM, John Stultz <john.stultz@...aro.org> wrote:
> On 03/19/2012 06:26 AM, Russell King - ARM Linux wrote:
>>
>> On Mon, Mar 19, 2012 at 06:49:34PM +0530, Ajeet Yadav wrote:
>>>
>>> Therefore our target configuration with 2.6 kernel was
>>> GENERIC_CLOCKEVENTS=y, ARCH_USES_GETTIMEOFFSET=y,
>>
>> It's absolutely absurd to have a platform converted to use clockevents
>> and clocksources, and then select ARCH_USES_GETTIMEOFFSET.  That's saying
>> "I provide the new infrastructure, but I want the dodgy old compatibility
>> which doesn't work properly with a set of other features as well".
>>
>>> I conclude that GENERIC_CLOCKEVENTS is supported, hence I must set
>>> ARCH_USES_GETTIMEOFFSET=n, in order to use NO_HZ, HIGH_RES_TIMERS,
>>> IRQSOFF_TRACER, PREEMPT_TRACER
>>
>> Correct.  If you're using clockevents and clocksources, you should not
>> select ARCH_USES_GETTIMEOFFSET.
>>
>
> Hey Ajeet,
>    As Russell pointed out, it looks like you're confused as to the use of
> ARCH_USES_GETTIMEOFFSET. That option is only for legacy systems that don't
> provide continuous clocksources that can be used for timekeeping.
>
> In the past, time was incremented by one tick every timer interrupt.  Some
> systems could use the timer hardware (usually PIT style decrementer) to
> calculate inter-tick times. Its only for this style of hardware, that either
> wraps or resets each tick, that GETTIMEOFFSET is needed.  If you have a
> continuous counter that doesn't wrap for a reasonable number of ticks, you
> want to use the clocksource abstraction to represent that hardware. That has
> the benefits of allowing high res timers and nohz, since we don't need to
> keep a constant tick-beat to keep time (and also avoids lost-ticks and a
> host of problems that tick based timekeeping can run into).
>
> So I suspect you probably want to verify your hardware supports a
> clocksource and disable ARCH_USES_GETTIMEOFFSET.
>
> Sorry for any confusion!
>
> thanks
> -john
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/