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    SubjectRe: [GIT PULL] adaptive spinning mutexes
    On Wed, 14 Jan 2009 21:51:22 +0100
    Ingo Molnar <mingo@elte.hu> wrote:

    >
    > * Andrew Morton <akpm@linux-foundation.org> 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 :(

    > > > Note that CONFIG_SCHED_DEBUG=y is also the default.
    > >
    > > akpm:/usr/src/25> echo $ARCH
    > > x86_64
    > > akpm:/usr/src/25> make defconfig
    > > *** Default configuration is based on 'x86_64_defconfig'
    >
    > x86 defconfig is used too, but it's a pretty rare usage.
    >
    > Under default i mean the customary meaning of default config: it's the
    > default if you come via 'make oldconfig' or if you derive your config from
    > a distro config:
    >
    > | config SCHED_DEBUG
    > | bool "Collect scheduler debugging info"
    > | depends on DEBUG_KERNEL && PROC_FS
    > | default y
    >

    This simply isn't reliable.


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