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sched: Remove rq->clock coupling from set_task_cpu()

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set_task_cpu() should be rq invariant and only touch task state, it
currently fails to do so, which opens up a few races, since not all
callers hold both rq->locks.

Remove the relyance on rq->clock, as any site calling set_task_cpu()
should also do a remote clock update, which should ensure the observed
time between these two cpus is monotonic, as per
kernel/sched_clock.c:sched_clock_remote().

Therefore we can simply remove the clock_offset bits and be happy.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-11-27 14:12:25 +01:00 committed by Ingo Molnar
parent 970b13bacb
commit 5afcdab706
1 changed files with 1 additions and 12 deletions
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13
kernel/sched.c
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@ -2060,23 +2060,12 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
void set_task_cpu(struct task_struct *p, unsigned int new_cpu) void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
{ {
int old_cpu = task_cpu(p); int old_cpu = task_cpu(p);
struct rq *old_rq = cpu_rq(old_cpu), *new_rq = cpu_rq(new_cpu); struct rq *old_rq = cpu_rq(old_cpu);
struct cfs_rq *old_cfsrq = task_cfs_rq(p), struct cfs_rq *old_cfsrq = task_cfs_rq(p),
*new_cfsrq = cpu_cfs_rq(old_cfsrq, new_cpu); *new_cfsrq = cpu_cfs_rq(old_cfsrq, new_cpu);
u64 clock_offset;
clock_offset = old_rq->clock - new_rq->clock;
trace_sched_migrate_task(p, new_cpu); trace_sched_migrate_task(p, new_cpu);
#ifdef CONFIG_SCHEDSTATS
if (p->se.wait_start)
p->se.wait_start -= clock_offset;
if (p->se.sleep_start)
p->se.sleep_start -= clock_offset;
if (p->se.block_start)
p->se.block_start -= clock_offset;
#endif
if (old_cpu != new_cpu) { if (old_cpu != new_cpu) {
p->se.nr_migrations++; p->se.nr_migrations++;
#ifdef CONFIG_SCHEDSTATS #ifdef CONFIG_SCHEDSTATS