From: khilman@deeprootsystems•com (Kevin Hilman)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH V2] [ARM] Add ARCH_PROVIDES_UDELAY config option
Date: Fri, 30 Apr 2010 15:11:20 -0700 [thread overview]
Message-ID: <87d3xgd20n.fsf@deeprootsystems.com> (raw)
In-Reply-To: <u2pd73d4eaf1004301237k3ceb859dobe74fe53abec774d@mail.gmail.com> (Colin Cross's message of "Fri\, 30 Apr 2010 12\:37\:40 -0700")
Colin Cross <ccross@android•com> writes:
> An alternative to this patch would be to add a config option to use
> sched_clock() to provide the counter instead of the cycle loop. The
> same loops_per_jiffy calibration could be done to determine the
> sched_clock frequency. Any machine with an available constant tick
> rate counter, which is likely to be used for sched_clock() already,
> can enable CONFIG_UDELAY_USES_SCHED_CLOCK.
Or even better, why not have an option to use the clocksource which is
most likely using the constant tick timer as well.
Kevin
> On Fri, Apr 30, 2010 at 12:12 PM, Colin Cross <ccross@android•com> wrote:
>> On SMP kernels, the loops_per_jiffy value is not scaled due to the
>> possibility of one CPU affecting the speed of another CPU while the
>> second CPU is in a udelay loop. ?Since loops_per_jiffy is calculated
>> once on boot for SMP kernels, udelays are too long if the CPU
>> frequency is scaled down from the boot frequency, or too short if the
>> frequency is scaled up. ?Some SOCs have a timer with a constant tick
>> rate that can be used to time udelays, similar to the TSC on x86.
>> Provide a config flag to allow these SOCs to override the default
>> ARM udelay implementation.
>>
>> Signed-off-by: Colin Cross <ccross@android•com>
next prev parent reply other threads:[~2010-04-30 22:11 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-30 19:12 [PATCH V2] [ARM] Add ARCH_PROVIDES_UDELAY config option Colin Cross
2010-04-30 19:37 ` Colin Cross
2010-04-30 22:11 ` Kevin Hilman [this message]
2010-05-01 0:04 ` Saravana Kannan
2010-05-01 10:01 ` Russell King - ARM Linux
2010-05-21 22:01 ` Saravana Kannan
2010-05-21 22:06 ` Russell King - ARM Linux
2010-05-21 22:10 ` Saravana Kannan
2010-05-28 0:41 ` Saravana Kannan
2010-06-22 1:14 ` Saravana Kannan
2010-06-28 2:30 ` Colin Cross
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