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Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched, x86: Avoid unnecessary overflow in sched_clock
  sched: Fix buglet in return_cfs_rq_runtime()
  sched: Avoid SMT siblings in select_idle_sibling() if possible
  sched: Set the command name of the idle tasks in SMP kernels
  sched, rt: Provide means of disabling cross-cpu bandwidth sharing
  sched: Document wait_for_completion_*() return values
  sched_fair: Fix a typo in the comment describing update_sd_lb_stats
  sched: Add a comment to effective_load() since it's a pain
This commit is contained in:
Linus Torvalds
2011-12-05 16:50:24 -08:00
parent 35337c8341 4cecf6d401
commit 7125faceab
6 changed files with 171 additions and 36 deletions
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23
arch/x86/include/asm/timer.h
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@@ -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;
}