ACPI: Be in TS_POLLING state during mwait based C-state entry
authorPallipadi, Venkatesh <venkatesh.pallipadi@intel.com>
Wed, 10 Feb 2010 18:35:31 +0000 (10:35 -0800)
committerLen Brown <len.brown@intel.com>
Mon, 22 Feb 2010 18:10:14 +0000 (13:10 -0500)
commitd306ebc28649b89877a22158fe0076f06cc46f60
tree9a054d9a01889acca64bf018ed1e4778db0d5e19
parent627fa177a1502ad24390d945851209ac022f3a36
ACPI: Be in TS_POLLING state during mwait based C-state entry

ACPI deep C-state entry had a long standing bug/missing feature, wherein we were sending
resched IPIs when an idle CPU is in mwait based deep C-state. Only mwait based C1 was using
the write to the monitored address to wake up mwait'ing CPU.

This patch changes the code to retain TS_POLLING bit if we are entering an mwait based
deep C-state.

The patch has been verified to reduce the number of resched IPIs in general and also
improves the performance/power on workloads with low system utilization (i.e., when mwait based
deep C-states are being used).

Fixes "netperf ~50% regression with 2.6.33-rc1, bisect to 1b9508f"
http://marc.info/?l=linux-kernel&m=126441481427331&w=4

Reported-by: Lin Ming <ming.m.lin@intel.com>
Tested-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
drivers/acpi/processor_idle.c