> -----Original Message----- > From: Will Deacon [mailto:[email protected]] > Sent: 2014年4月15日 20:50 > To: Neil Zhang > Cc: [email protected]; [email protected]; > [email protected]; Sudeep Holla > 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 <[email protected]> > > > > > > > > > > > > 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). >
Thanks for the comments, I will refine it according to your suggestion. > Will Best Regards, Neil Zhang
