Messages in this thread | | | Date | Tue, 15 Apr 2014 13:49:53 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v2] ARM: perf: save/restore pmu registers in pm notifier |
| |
On Tue, Apr 15, 2014 at 01:46:08PM +0100, Neil Zhang wrote: > > On Tue, Apr 15, 2014 at 01:37:17PM +0100, Neil Zhang wrote: > > > > On Mon, Apr 14, 2014 at 02:42:22AM +0100, Neil Zhang wrote: > > > > > From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> > > > > > > > > > > This adds core support for saving and restoring CPU PMU registers > > > > > for suspend/resume support i.e. deeper C-states in cpuidle terms. > > > > > This patch adds support only to ARMv7 PMU registers save/restore. > > > > > It needs to be extended to xscale and ARMv6 if needed. > > > > > > > > > > [Neil] We found that DS-5 not work on our CA7 based SoCs. > > > > > After debuging, found PMU registers were lost because of core power > > down. > > > > > Then i found Sudeep had a patch to fix it about two years ago but > > > > > not in the mainline, just port it. > > > > > > > > What I don't like about this patch is that we're introducing > > > > significant overhead for SoCs that don't require save/restore of the > > > > PMU state. I'd much rather see core power down disabled whilst the > > > > PMU is in use but, if that's not possible, then I think we need to: > > > > > > > > (1) Make this conditional for cores that really need it > > > > > > > > (2) Only save/restore if the PMU is in use (even better, just save/restore > > > > the live registers, but that's probably not worth the effort > > > > initially). > > > > > > > > > > The patch has check the ARMV7_PMNC_E bit when save / restore, so > > > suppose only the core's that use PMU will do the save / restore work. > > > > Seems pretty fragile to base our save/restore decision on the value of one of > > the registers, though. What happens if the control register is zeroed by the > > core power down? > > > It will check the saved control value when restore, so is should be OK > while control register is zeroed.
Ah yes, I mixed up and save and restore functions. It's still horrible that we have to read the control register unconditionally during the save though -- it might be nicer if we simply register/unregister the notifier during perf runs (in the same way that we request/free the PMU IRQs).
Will
| |