Thomas Gleixner wrote:
Problem description at:
http://bugzilla.kernel.org/show_bug.cgi?id=8048
Commit b18ec80396834497933d77b81ec0918519f4e2a7
[PATCH] sched: improve migration accuracy
optimized the scheduler time calculations, but broke posix-cpu-timers.
The problem is that the p->last_ran value is not updated after a context
switch. So a subsequent call to current_sched_time() calculates with a
stale p->last_ran value, i.e. accounts the full time, which the task was
scheduled away.
Could you expand on the impact of this bug for non-kernel hackers? :-)
I'm currently testing 2.6.20-rt5. My app runs in SCHED_RR and just
blocks waiting for several signals. Since my app is the only SCHED_RR
process running on the system, I get the impression that I'm not
affected by this bug. Is that correct?
Signed-off-by: Thomas Gleixner <[email protected]>
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -3566,7 +3566,7 @@ switch_tasks:
sched_info_switch(prev, next);
if (likely(prev != next)) {
- next->timestamp = now;
+ next->timestamp = next->last_ran = now;
rq->nr_switches++;
rq->curr = next;
++*switch_count;
Regards,
John
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