50 Watt idle power regression bisected to Linux-3.10
From: Len Brown
Date: Sat Dec 07 2013 - 03:00:14 EST
An idle WSM-EX box (40 Xeon cores) runs 50 Watts hotter after this patch:
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Thu Mar 21 22:50:03 2013 +0100
x86: Use generic idle loop
ie. the commit before this patch (aba92c9e2cf3042bf6efc68fa2e4235ba01bf499)
runs at 50 watts less, as do Linux 3.7, 3.8 and 3.9.
The difference is that the good kernels allow about 98% residence
in the package C6 state, while the bad kernel is so noisy that it
gets into pc6 0% of the time.
(indeed, even core C6 is reduced to about 50% from over 99%)
No, Linux-3.13-rc3 does not fix this issue, even though it contains
the following patch, claiming to address an issue with the commit above:
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed Sep 11 12:43:13 2013 +0200
sched, idle: Fix the idle polling state logic
Mike reported that commit 7d1a9417 ("x86: Use generic idle loop")
regressed several workloads and caused excessive reschedule
The patch in question failed to notice that the x86 code had an
inverted sense of the polling state versus the new generic code (x86:
default polling, generic: default !polling).
Fix the two prominent x86 mwait based idle drivers and introduce a few
new generic polling helpers (fixing the wrong smp_mb__after_clear_bit
Also switch the idle routines to using tif_need_resched() which is an
immediate TIF_NEED_RESCHED test as opposed to need_resched which will
end up being slightly different.
Reported-by: Mike Galbraith <bitbucket@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
How shall we proceed?
-Len Brown, Intel Open Source Technology Center
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/