Messages in this thread | | | Date | Mon, 28 Jun 2021 15:29:05 +0800 | From | Leo Yan <> | Subject | Re: [PATCH] perf arm-spe: Fix incorrect sample timestamp in perf script |
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On Mon, Jun 28, 2021 at 02:30:56PM +0800, Yang Jihong wrote: > Hello Leo, > > On 2021/6/28 12:07, Leo Yan wrote: > > On Mon, Jun 28, 2021 at 11:45:07AM +0800, Yang Jihong wrote: > > > > [...] > > > > > The timestamp does not match. Each timestamp has a difference of > > > 213.98296702 seconds. Is the command I executed wrong? > > > > I don't understand what's your meaning "a difference of 213.98296702 > > seconds". > > > > But let me give an explaination with your below examples. You could > > the command "perf script" outputs the timestamp 314938.859071370 which > > is the kernel's timestamp, if using the command "perf script -D", it > > outputs the value 31515284203839 which is the Arch timer's raw counter > > value. > > > > In theory, the arch timer's counter is enabled at the very early > > time before kernel's booting (e.g. bootloaders, UEFI, etc...). So for > > the kernel's timestamp, it should calibrate the timestamp and reduce > > the offset prior to the kernel's booting. I think this is the reason > > why you observed 213.98296702 seconds difference (if compared with > > your own patch?) > > > > If still see any issue, please let me know. Thanks a lot for the > > testing! > > > Thanks for the very detailed explanation. > To keep the correct relative time sequence between events in SPE and other > events, we should use kernel timestamp instead of arch time. Therefore, we > need to calibrate the time. Is this correct?
Yes, correct!
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