x86, mtrr, pat: Fix one cpu getting out of sync during resume
On laptops with core i5/i7, there were reports that after resume
graphics workloads were performing poorly on a specific AP, while
the other cpu's were ok. This was observed on a 32bit kernel
specifically.
Debug showed that the PAT init was not happening on that AP
during resume and hence it contributing to the poor workload
performance on that cpu.
On this system, resume flow looked like this:
1. BP starts the resume sequence and we reinit BP's MTRR's/PAT
early on using mtrr_bp_restore()
2. Resume sequence brings all AP's online
3. Resume sequence now kicks off the MTRR reinit on all the AP's.
4. For some reason, between point 2 and 3, we moved from BP
to one of the AP's. My guess is that printk() during resume
sequence is contributing to this. We don't see similar
behavior with the 64bit kernel but there is no guarantee that
at this point the remaining resume sequence (after AP's bringup)
has to happen on BP.
5. set_mtrr() was assuming that we are still on BP and skipped the
MTRR/PAT init on that cpu (because of 1 above)
6. But we were on an AP and this led to not reprogramming PAT
on this cpu leading to bad performance.
Fix this by doing unconditional mtrr_if->set_all() in set_mtrr()
during MTRR/PAT init. This might be unnecessary if we are still
running on BP. But it is of no harm and will guarantee that after
resume, all the cpu's will be in sync with respect to the
MTRR/PAT registers.
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1301438292-28370-1-git-send-email-eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>
Tested-by: Keith Packard <keithp@keithp.com>
Cc: stable@kernel.org [v2.6.32+]
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
1 file changed