psi: clarify the Kconfig text for the default-disable option
The current help text caused some confusion in online forums about
whether or not to default-enable or default-disable psi in vendor
kernels. This is because it doesn't communicate the reason for why we
made this setting configurable in the first place: that the overhead is
non-zero in an artificial scheduler stress test.
Since this isn't representative of real workloads, and the effect was
not measurable in scheduler-heavy real world applications such as the
webservers and memcache installations at Facebook, it's fair to point
out that this is a pretty cautious option to select.
Link: http://lkml.kernel.org/r/20190129233617.16767-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/init/Kconfig b/init/Kconfig
index 3541466..c9386a3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -512,6 +512,17 @@
per default but can be enabled through passing psi=1 on the
kernel commandline during boot.
+ This feature adds some code to the task wakeup and sleep
+ paths of the scheduler. The overhead is too low to affect
+ common scheduling-intense workloads in practice (such as
+ webservers, memcache), but it does show up in artificial
+ scheduler stress tests, such as hackbench.
+
+ If you are paranoid and not sure what the kernel will be
+ used for, say Y.
+
+ Say N if unsure.
+
endmenu # "CPU/Task time and stats accounting"
config CPU_ISOLATION
