Doug Anderson
3252a646aa
clocksource: exynos_mct: Only use 32-bits where possible ...
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: Doug Anderson <dianders@chromium.org>
Acked-by Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
2014-07-23 12:02:41 +02:00
Merge branch 'acpi-video'
2014-07-10 21:04:25 +02:00
ahci_xgene: fix the dma state machine lockup for the IDENTIFY DEVICE PIO mode command.
2014-07-08 11:46:05 -04:00
atm: fore200e.c: Cleaning up uninitialized variables
2014-06-02 17:11:03 -07:00
DMA, CMA: fix possible memory leak
2014-06-23 16:47:44 -07:00
zram: revalidate disk after capacity change
2014-07-03 09:21:53 -07:00
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
2014-06-12 14:27:40 -07:00
bus/arm-cci: add dependency on OF && CPU_V7
2014-06-17 17:09:35 +02:00
Merge branch 'for-linus' of git://git.kernel.dk/linux-block
2014-06-11 08:41:17 -07:00
i8k: Fix non-SMP operation
2014-07-09 16:45:36 -07:00
This batch of fixes is for a handful of clock drivers from Allwinner,
2014-07-13 12:21:04 -07:00
clocksource: exynos_mct: Only use 32-bits where possible
2014-07-23 12:02:41 +02:00
Char / misc driver patches for 3.16-rc1
2014-06-03 08:06:56 -07:00
cpufreq: Makefile: fix compilation for davinci platform
2014-07-09 02:54:15 +02:00
cpuidle: mvebu: Fix the name of the states
2014-06-18 21:54:46 +02:00
crypto: caam - fix memleak in caam_jr module
2014-07-10 16:59:13 +08:00
Update imx-sdma cyclic handling to report residue
2014-07-01 12:23:42 +05:30
PCI changes for the v3.16 merge window:
2014-06-02 12:15:19 -07:00
firewire: Use ktime_get_ts()
2014-06-12 16:18:45 +02:00
efi-pstore: Fix an overflow on 32-bit builds
2014-06-27 07:30:32 +01:00
gpio: of: Fix handling for deferred probe for -gpio suffix
2014-06-12 09:57:00 +02:00
Merge branch 'drm-fixes' of git://people.freedesktop.org/~airlied/linux
2014-07-10 20:37:33 -07:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid
2014-07-07 13:13:03 -07:00
hsi: omap_ssi_port: use normal module refcounting
2014-06-05 00:59:05 +02:00
Drivers: hv: util: Fix a bug in the KVP code
2014-07-09 14:34:35 -07:00
hwmon: (adc128d818) Drop write support on inX_input attributes
2014-07-07 09:48:23 -07:00
i2c: sun6i-p2wi: Remove duplicate inclusion of module.h
2014-06-27 14:39:36 +02:00
iio: ti_am335x_adc: Fix: Use same step id at FIFOs both ends
2014-07-08 21:21:22 +01:00
Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending
2014-06-12 22:38:32 -07:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
2014-06-09 18:46:02 -07:00
iommu/amd: Fix small race between invalidate_range_end/start
2014-06-20 16:14:22 +02:00
irqchip: spear_shirq: Fix interrupt offset
2014-06-21 23:26:39 +00:00
isdn: hisax: Drop duplicate Kconfig entry
2014-06-16 21:31:37 -07:00
Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/cooloney/linux-leds
2014-06-12 13:08:09 -07:00
powerpc/macintosh/smu.c: Fix closing brace followed by if
2014-06-24 12:43:15 +10:00
. Fix DM multipath IO hang regression from 3.15 due to logic bug in
2014-07-11 09:33:36 -07:00
Merge branch 'topic/omap3isp' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
2014-06-12 23:04:28 -07:00
drivers/memstick/host/rtsx_pci_ms.c: add cancel_work when remove driver
2014-06-23 16:47:44 -07:00
mfd: ab8500: Fix dt irq mapping
2014-06-26 13:34:15 +01:00
ARM: SoC fixes for 3.16
2014-06-25 12:19:01 -07:00
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
2014-06-12 14:27:40 -07:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
2014-06-12 10:30:18 -07:00
net: allwinner: emac: Add missing free_irq
2014-06-25 16:31:17 -07:00
kernel/printk: use symbolic defines for console loglevels
2014-06-04 16:54:17 -07:00
of: Provide a function to request and map memory
2014-07-23 12:02:30 +02:00
parport: convert use of typedef ctl_table to struct ctl_table
2014-06-06 16:08:15 -07:00
PCI: Fix unaligned access in AF transaction pending test
2014-06-17 15:40:13 -06:00
USB fixes for 3.16-rc5
2014-07-12 14:13:10 -07:00
pinctrl: berlin: fix an error code in berlin_pinctrl_probe()
2014-07-05 01:15:35 +02:00
Merge branch 'for_linus' of git://cavan.codon.org.uk/platform-drivers-x86
2014-06-10 16:58:32 -07:00
Merge branches 'pnp', 'powercap', 'pm-runtime' and 'pm-opp'
2014-06-03 23:13:00 +02:00
ACPI and power management updates for 3.16-rc1
2014-06-04 08:57:16 -07:00
ptp: ptp_pch depends on x86_32
2014-06-17 15:43:48 -07:00
pwm: Changes for v3.16-rc1
2014-06-11 14:06:55 -07:00
rapidio/tsi721: use pci_enable_msix_exact() instead of pci_enable_msix()
2014-06-06 16:08:13 -07:00
Merge remote-tracking branches 'regulator/fix/bcm590xx', 'regulator/fix/palmas' and 'regulator/fix/tps65218' into regulator-linus
2014-06-28 14:01:04 +01:00
remoteproc: da8xx: don't select CMA on no-MMU
2014-06-17 17:09:36 +02:00
ARM: SoC driver changes
2014-06-02 16:35:49 -07:00
drivers/rtc/rtc-puv3.c: remove "&dev->" for typo issue MIME-Version: 1.0
2014-06-20 08:22:39 +08:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
2014-06-21 06:47:01 -10:00
SCSI for-linus on 20140705
2014-07-06 12:08:30 -07:00
SH Driver Update for v3.16
2014-06-06 11:44:09 -07:00
Merge remote-tracking branches 'spi/fix/pxa2xx', 'spi/fix/qup' and 'spi/fix/sh-sci' into spi-linus
2014-06-28 14:01:23 +01:00
Second set of IIO fixes for the 3.16 cycle.
2014-06-29 09:43:23 -07:00
iscsi-target: fix iscsit_del_np deadlock on unload
2014-06-27 23:23:35 -07:00
TC: Handle device_register() errors.
2014-06-26 10:48:23 +01:00
thermal: ti-soc-thermal: ti-bandgap.c: Cleaning up wrong address is checked
2014-07-01 09:52:35 +08:00
serial: imx: Fix build breakage
2014-07-11 17:43:13 -07:00
Revert "uio: fix vma io range check in mmap"
2014-06-17 16:07:08 -07:00
USB: serial: ftdi_sio: Add Infineon Triboard
2014-07-11 18:22:38 -07:00
A handful of VFIO bug fixes for v3.16
2014-06-07 20:12:15 -07:00
vhost-scsi: don't open-code kvfree
2014-06-23 09:22:48 +03:00
fb: adv7393: add missing semicolon
2014-07-01 13:18:38 +03:00
w1: mxc_w1: Fix incorrect "presence" status
2014-06-19 17:51:46 -07:00
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
2014-06-21 06:47:01 -10:00
xen: regression and PVH fixes for 3.16-rc1
2014-06-19 07:53:27 -10:00
Char / misc driver patches for 3.16-rc1
2014-06-03 08:06:56 -07:00
3252a646aa