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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> |
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