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authorPeter Zijlstra <peterz@infradead.org>2013-11-18 18:27:06 +0100
committerIngo Molnar <mingo@kernel.org>2013-12-11 15:52:35 +0100
commit9dbdb155532395ba000c5d5d187658b0e17e529f (patch)
treea01fb4066fbad520f364abc0bb7b68f45aab3100 /include/linux/sched.h
parentbe5e610c0fd6ef772cafb9e0bd4128134804aef3 (diff)
sched/fair: Rework sched_fair time accounting
Christian suffers from a bad BIOS that wrecks his i5's TSC sync. This results in him occasionally seeing time going backwards - which crashes the scheduler ... Most of our time accounting can actually handle that except the most common one; the tick time update of sched_fair. There is a further problem with that code; previously we assumed that because we get a tick every TICK_NSEC our time delta could never exceed 32bits and math was simpler. However, ever since Frederic managed to get NO_HZ_FULL merged; this is no longer the case since now a task can run for a long time indeed without getting a tick. It only takes about ~4.2 seconds to overflow our u32 in nanoseconds. This means we not only need to better deal with time going backwards; but also means we need to be able to deal with large deltas. This patch reworks the entire code and uses mul_u64_u32_shr() as proposed by Andy a long while ago. We express our virtual time scale factor in a u32 multiplier and shift right and the 32bit mul_u64_u32_shr() implementation reduces to a single 32x32->64 multiply if the time delta is still short (common case). For 64bit a 64x64->128 multiply can be used if ARCH_SUPPORTS_INT128. Reported-and-Tested-by: Christian Engelmayer <cengelma@gmx.at> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: fweisbec@gmail.com Cc: Paul Turner <pjt@google.com> Cc: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/20131118172706.GI3866@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/sched.h')
-rw-r--r--include/linux/sched.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 96d674ba3876..53f97eb8dbc7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -930,7 +930,8 @@ struct pipe_inode_info;
struct uts_namespace;
struct load_weight {
- unsigned long weight, inv_weight;
+ unsigned long weight;
+ u32 inv_weight;
};
struct sched_avg {