* Ingo Molnar <mingo@xxxxxxx> 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. > > 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. Another test would be to build the scheduler latency tracer into your kernel: CONFIG_SCHED_TRACER=y And enable it via: echo wakeup > /debug/tracing/current_tracer and you should be seeing the worst-case scheduling latency traces in /debug/tracing/trace, and the largest observed latency will be in /debug/tracing/tracing_max_latency [in microseconds]. You can reset the max-latency (and thus restart tracing) via: echo 0 > /debug/tracing/tracing_max_latency Latencies up to 100 microseconds are ok. If you see 10 seconds delays there (values of 10,000,000 or more) then it's probably a scheduler bug. Please reproduce the latency under KVM and send us the trace. The trace file will be a lot more verbose and a lot more verbose if you also enable the function tracer (FUNCTION_TRACER, DYNAMIC_FTRACE and FUNCTION_GRAPH_TRACER). 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
