Messages in this thread | | | Subject | Re: [PATCH] perf arm-spe: Fix incorrect sample timestamp in perf script | From | Yang Jihong <> | Date | Tue, 29 Jun 2021 08:53:55 +0800 |
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Hello Leo,
On 2021/6/28 15:29, Leo Yan wrote: > 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! I see. Thank you for your answer.:)
Jihong > . >
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