diff options
| author | Rafael J. Wysocki <rjw@sisk.pl> | 2011-12-21 09:51:23 +0100 |
|---|---|---|
| committer | Rafael J. Wysocki <rjw@sisk.pl> | 2011-12-21 09:51:23 +0100 |
| commit | dfa9d178cd28caf5d76bc4f37f4b3e7e8df8e697 (patch) | |
| tree | d97ca7790d8a622cba9fdd19832decdb0aa6418a /arch/x86/include/asm/timer.h | |
| parent | 3f19f08a7ec74cfc50fbad3c5e615760afbd23a0 (diff) | |
| parent | 7b4050381127ae11fcfc74a106d715a5fbbf888a (diff) | |
Merge branch 'devfreq-for-next' of git://git.infradead.org/users/kmpark/linux-samsung into pm-devfreq
* 'devfreq-for-next' of git://git.infradead.org/users/kmpark/linux-samsung: (765 commits)
PM/Devfreq: Add Exynos4-bus device DVFS driver for Exynos4210/4212/4412.
pci: Fix hotplug of Express Module with pci bridges
i2c-eg20t: correct the driver init order of pch_i2c_probe()
I2C: OMAP: fix FIFO usage for OMAP4
i2c-s3c2410: Fix return code of s3c24xx_i2c_parse_dt_gpio
i2c: i2c-s3c2410: Add a cpu_relax() to busy wait for bus idle
Linux 3.2-rc6
Revert "drm/i915: fix infinite recursion on unbind due to ilk vt-d w/a"
btrfs: lower the dirty balance poll interval
drm/i915/dp: Dither down to 6bpc if it makes the mode fit
drm/i915: enable semaphores on per-device defaults
drm/i915: don't set unpin_work if vblank_get fails
drm/i915: By default, enable RC6 on IVB and SNB when reasonable
iommu: Export intel_iommu_enabled to signal when iommu is in use
drm/i915/sdvo: Include LVDS panels for the IS_DIGITAL check
drm/i915: prevent division by zero when asking for chipset power
drm/i915: add PCH info to i915_capabilities
drm/i915: set the right SDVO transcoder for CPT
drm/i915: no-lvds quirk for ASUS AT5NM10T-I
sched: Fix select_idle_sibling() regression in selecting an idle SMT sibling
...
Diffstat (limited to 'arch/x86/include/asm/timer.h')
| -rw-r--r-- | arch/x86/include/asm/timer.h | 23 |
1 files changed, 22 insertions, 1 deletions
diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h index fa7b9176b76c..431793e5d484 100644 --- a/arch/x86/include/asm/timer.h +++ b/arch/x86/include/asm/timer.h @@ -32,6 +32,22 @@ extern int no_timer_check; * (mathieu.desnoyers@polymtl.ca) * * -johnstul@us.ibm.com "math is hard, lets go shopping!" + * + * In: + * + * ns = cycles * cyc2ns_scale / SC + * + * Although we may still have enough bits to store the value of ns, + * in some cases, we may not have enough bits to store cycles * cyc2ns_scale, + * leading to an incorrect result. + * + * To avoid this, we can decompose 'cycles' into quotient and remainder + * of division by SC. Then, + * + * ns = (quot * SC + rem) * cyc2ns_scale / SC + * = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC + * + * - sqazi@google.com */ DECLARE_PER_CPU(unsigned long, cyc2ns); @@ -41,9 +57,14 @@ DECLARE_PER_CPU(unsigned long long, cyc2ns_offset); static inline unsigned long long __cycles_2_ns(unsigned long long cyc) { + unsigned long long quot; + unsigned long long rem; int cpu = smp_processor_id(); unsigned long long ns = per_cpu(cyc2ns_offset, cpu); - ns += cyc * per_cpu(cyc2ns, cpu) >> CYC2NS_SCALE_FACTOR; + quot = (cyc >> CYC2NS_SCALE_FACTOR); + rem = cyc & ((1ULL << CYC2NS_SCALE_FACTOR) - 1); + ns += quot * per_cpu(cyc2ns, cpu) + + ((rem * per_cpu(cyc2ns, cpu)) >> CYC2NS_SCALE_FACTOR); return ns; } |