* Kevin Shanahan <kmshanah@xxxxxxxxxxx> wrote: > On Tue, 2009-01-20 at 13:56 +0100, Ingo Molnar wrote: > > * Kevin Shanahan <kmshanah@xxxxxxxxxxx> wrote: > > > > This suggests some sort of KVM-specific problem. Scheduler latencies > > > > in the seconds that occur under normal load situations are noticed and > > > > reported quickly - and there are no such open regressions currently. > > > > > > It at least suggests a problem with interaction between the scheduler > > > and kvm, otherwise reverting that scheduler patch wouldn't have made the > > > regression go away. > > > > the scheduler affects almost everything, so almost by definition a > > scheduler change can tickle a race or other timing bug in just about any > > code - and reverting that change in the scheduler can make the bug go > > away. But yes, it could also be a genuine scheduler bug - that is always a > > possibility. > > Okay, I understand. > > > Could you please run a cfs-debug-info.sh session on a CONFIG_SCHED_DEBUG=y > > and CONFIG_SCHEDSTATS=y kernel, while you are experiencing those > > latencies: > > > > http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh > > > > and post that (relatively large) somewhere, or send it as a reply after > > bzip2 -9 compressing it? It will include a lot of information about the > > delays your tasks are experiencing. > > Running it while the problem is occuring will be tricky, as it only > lasts for a few seconds at a time. Is it going to be useful at all to > just see those statistics if the system is running normally? > > I might need to modify the script a little. Am I right that everything > above "gathering statistics..." is pretty much static information? Correct. > I could run top, vmstat and cat /proc/sched_debug in a loop until the > problem occurs and then trim it. Something like: > > while true; do > date >> $FILE > echo "-- top: --" >> $FILE > top -H -c -b -d 1 -n 0.5 >> $FILE 2>/dev/null > echo "-- vmstat: --" >> $FILE > vmstat >> $FILE 2>/dev/null > echo "-- sched_debug #$i: --" >> $FILE > cat /proc/sched_debug >> $FILE 2>/dev/null > done > > That should take a snapshot every half second or so. Yeah, that would be lovely. You dont even have to trim it much - just give us a timestamp to look at for the delay incident. You might also want to start the kvm session while the script is already running - that way we'll get fresh statistics and see the whole thing. Ingo -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
