On Tue, Aug 18, 2020 at 10:24:13PM +0530, Muni Sekhar wrote: > On Tue, Aug 18, 2020 at 8:06 PM Greg KH <greg@xxxxxxxxx> wrote: > > > > On Tue, Aug 18, 2020 at 08:00:11PM +0530, Muni Sekhar wrote: > > > Hi all, > > > > > > I’ve two identical Linux systems with only kernel differences. > > > > What are the differences in the kernels? You didn't answer this question, is this the same kernel source being compared here? Same version? Same compiler? Everything identical? > > > While doing kernel profiling with perf, I got the below mentioned > > > metrics for Scheduler benchmarks. > > > > > > 1st system (older kernel version compared to the other system) benchmark result: > > > > > > $ perf bench sched messaging -g 64 > > > # Running 'sched/messaging' benchmark: > > > # 20 sender and receiver processes per group > > > # 64 groups == 2560 processes run > > > > > > Total time: 2.936 [sec] > > > > > > > > > 2nd system benchmark result: > > > > > > $ perf bench sched messaging -g 64 > > > # Running 'sched/messaging' benchmark: > > > # 20 sender and receiver processes per group > > > # 64 groups == 2560 processes run > > > > > > Total time: 10.074 [sec] > > > > > > > > > So as per scheduler benchmark results, clearly a huge difference > > > between two systems. > > > Can anyone suggest to me how to dive deeper to know the root cause for > > > it. > > > > Look a the differences between your different kernels, that would be a > > great start :) > I created the difference between two kernel config files and then > tried to spot the CONFIG*SCHED* differences. > Interestingly I see the difference in I/O scheduler config, 1st system > is set to “deadline” and other one is set to “cfq”. So I made it equal > by echoing to “/sys/block/<disk device>/queue/scheduler" but still no > change in scheduler benchmark metrics. > > Is it the correct way to find the differences between kernels? If so, > what other important CONFIG_* variables need to consider? > > > $ cat config.patch | grep -i sched > > CONFIG_HAVE_UNSTABLE_SCHED_CLOCK=y > CONFIG_CGROUP_SCHED=y > CONFIG_FAIR_GROUP_SCHED=y > # CONFIG_RT_GROUP_SCHED is not set > # IO Schedulers > @@ -369,10 +434,14 @@ CONFIG_IOSCHED_NOOP=y > CONFIG_IOSCHED_DEADLINE=y > CONFIG_IOSCHED_CFQ=y > CONFIG_CFQ_GROUP_IOSCHED=y > -CONFIG_DEFAULT_IOSCHED="deadline" > +CONFIG_DEFAULT_IOSCHED="cfq" > +CONFIG_MQ_IOSCHED_DEADLINE=m > +CONFIG_MQ_IOSCHED_KYBER=m > +CONFIG_IOSCHED_BFQ=m > +CONFIG_BFQ_GROUP_IOSCHED=y > CONFIG_SCHED_SMT=y > CONFIG_SCHED_MC=y > +CONFIG_SCHED_MC_PRIO=y > +# CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL is not set > +CONFIG_CPU_FREQ_GOV_SCHEDUTIL=y There's lots of other options that affect performance, depending on your specific benchmark, other than these. good luck! greg k-h _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
