* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 14 Jan 2009 21:51:22 +0100 > Ingo Molnar <mingo@xxxxxxx> wrote: > > > > > * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > Do people enable CONFIG_SCHED_DEBUG? > > > > > > > > If they suspect performance problems and want to analyze them? > > > > > > The vast majority of users do not and usually cannot compile their own > > > kernels. > > > > ... which they derive from distro kernels or some old .config they always > > used, via 'make oldconfig'. You are arguing against well-established facts > > here. > > > > If you dont believe my word for it, here's an analysis of all kernel > > configs posted to lkml in the past 8 months: > > > > $ grep ^CONFIG_SCHED_DEBUG linux-kernel | wc -l > > 424 > > > > $ grep 'CONFIG_SCHED_DEBUG is not' linux-kernel | wc -l > > 109 > > > > i.e. CONFIG_SCHED_DEBUG=y is set in 80% of the configs. A large majority > > of testers has it enabled and /sys/debug/sched_features was always a good > > mechanism that we used for runtime toggles. > > You just disproved your own case :( how so? 80% is not enough? I also checked Fedora and it has SCHED_DEBUG=y in its kernel rpms. note that there's also a performance issue here: we generally _dont want_ a debug sysctl overhead in the mutex code or in any fastpath for that matter. So making it depend on SCHED_DEBUG is useful. sched_feat() features get optimized out at build time when SCHED_DEBUG is disabled. So it gives us the best of two worlds: the utility of sysctls in the SCHED_DEBUG=y, and they get compiled out in the !SCHED_DEBUG case. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
