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| author | Mauro Carvalho Chehab <mchehab@redhat.com> | 2011-12-30 13:59:37 -0200 |
|---|---|---|
| committer | Mauro Carvalho Chehab <mchehab@redhat.com> | 2011-12-30 13:59:37 -0200 |
| commit | b4d48c942c17ce3d3a330ad91e109e522bc97378 (patch) | |
| tree | 3365292f3a5a502edb51492d011fd326c930ca40 /arch/x86/include/asm/timer.h | |
| parent | 1a5cd29631a6b75e49e6ad8a770ab9d69cda0fa2 (diff) | |
| parent | 5f0a6e2d503896062f641639dacfe5055c2f593b (diff) | |
Merge tag 'v3.2-rc7' into staging/for_v3.3
Linux 3.2-rc7
* tag 'v3.2-rc7': (1304 commits)
Linux 3.2-rc7
netfilter: xt_connbytes: handle negation correctly
Btrfs: call d_instantiate after all ops are setup
Btrfs: fix worker lock misuse in find_worker
net: relax rcvbuf limits
rps: fix insufficient bounds checking in store_rps_dev_flow_table_cnt()
net: introduce DST_NOPEER dst flag
mqprio: Avoid panic if no options are provided
bridge: provide a mtu() method for fake_dst_ops
md/bitmap: It is OK to clear bits during recovery.
md: don't give up looking for spares on first failure-to-add
md/raid5: ensure correct assessment of drives during degraded reshape.
md/linear: fix hot-add of devices to linear arrays.
sparc64: Fix MSIQ HV call ordering in pci_sun4v_msiq_build_irq().
pata_of_platform: Add missing CONFIG_OF_IRQ dependency.
ipv4: using prefetch requires including prefetch.h
VFS: Fix race between CPU hotplug and lglocks
vfs: __read_cache_page should use gfp argument rather than GFP_KERNEL
USB: Fix usb/isp1760 build on sparc
net: Add a flow_cache_flush_deferred function
...
Conflicts:
drivers/media/common/tuners/tda18218.c
drivers/media/video/omap3isp/ispccdc.c
drivers/staging/media/as102/as102_drv.h
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; } |