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  1. 24 7月, 2014 36 次提交
  3. 23 7月, 2014 4 次提交
    • T
      Merge branch 'clockevents/3.17' of... · 1af447bd
      由 Thomas Gleixner 提交于 
      Merge branch 'clockevents/3.17' of git://git.linaro.org/people/daniel.lezcano/linux into timers/core

Pull clockevents from Danel Lezcano:
 * New timer driver for the Cirrus Logic CLPS711X SoC
 * New driver for the Mediatek SoC which includes:
 * A new function for of, acked by Rob Herring
 * Move the PXA driver to drivers/clocksource, add DT support
 * Optimization of the exynos_mct driver
 * DT support for the renesas timers family.
 * Some Kconfig and driver fixlets
      1af447bd
    • D
      clocksource: exynos_mct: Only use 32-bits where possible · 3252a646
      由 Doug Anderson 提交于 
      The MCT has a nice 64-bit counter.  That means that we _can_ register
as a 64-bit clocksource and sched_clock.  ...but that doesn't mean we
should.

The 64-bit counter is read by reading two 32-bit registers.  That
means reading needs to be something like:
- Read upper half
- Read lower half
- Read upper half and confirm that it hasn't changed.

That wouldn't be terrible, but:
- THe MCT isn't very fast to access (hundreds of nanoseconds).
- The clocksource is queried _all the time_.

In total system profiles of real workloads on ChromeOS, we've seen
exynos_frc_read() taking 2% or more of CPU time even after optimizing
the 3 reads above to 2 (see below).

The MCT is clocked at ~24MHz on all known systems.  That means that
the 32-bit half of the counter rolls over every ~178 seconds.  This
inspired an optimization in ChromeOS to cache the upper half between
calls, moving 3 reads to 2.  ...but we can do better!  Having a 32-bit
timer that flips every 178 seconds is more than sufficient for Linux.
Let's just use the lower half of the MCT.

Times on 5420 to do 1000000 gettimeofday() calls from userspace:
* Original code:                      1323852 us
* ChromeOS cache upper half:          1173084 us
* ChromeOS + ldmia to optimize:       1045674 us
* Use lower 32-bit only (this code):  1014429 us

As you can see, the time used doesn't increase linearly with the
number of reads and we can make 64-bit work almost as fast as 32-bit
with a bit of assembly code.  But since there's no real gain for
64-bit, let's go with the simplest and fastest implementation.

Note: with this change roughly half the time for gettimeofday() is
spent in exynos_frc_read().  The rest is timer / system call overhead.

Also note: this patch disables the use of the MCT on ARM64 systems
until we've sorted out how to make "cycles_t" always 32-bit.  Really
ARM64 systems should be using arch timers anyway.
Signed-off-by: NDoug Anderson <dianders@chromium.org>
Acked-by Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
      3252a646
    • D
      clocksource: exynos_mct: Use readl_relaxed/writel_relaxed · fdb06f66
      由 Doug Anderson 提交于 
      Using the __raw functions is discouraged.  Update the file to
consistently use the proper functions.
Signed-off-by: NDoug Anderson <dianders@chromium.org>
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
      fdb06f66
    • R
      ARM: pxa: Add non device-tree timer link to clocksource · a38b1f60
      由 Robert Jarzmik 提交于 
      As clocksource pxa_timer was moved to clocksource framework, the
pxa_timer initialization needs to be a bit amended, to pass the
necessary informations to clocksource, ie :
 - the timer interrupt (mach specific)
 - the timer registers base (ditto)
 - the timer clockrate
Signed-off-by: NRobert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
      a38b1f60