Re: [PATCH v2 0/7] perf arm-spe: Enable timestamp

[Leo Yan]

Hi Al,

On Tue, Apr 06, 2021 at 09:38:32AM +0000, Al Grant wrote:

[...]

> > This patch set is to enable timestamp for Arm SPE trace.  It reads out TSC
> > parameters from mmap page and stores into auxtrace info structure;
> 
> Why not synthesize a PERF_RECORD_TIME_CONV - isn't that specifically to
> capture the TSC parameters from the mmap page? If a generic mechanism
> exists it would be better to use it, otherwise we'll have to do this again for
> future trace formats.

Good point!  Actually "perf record" tool has synthesized event
PERF_RECORD_TIME_CONV.  This patch series is studying the
implementation from Intel-PT, so the question is why the existed
implementations (like Intel-PT, Intel-BTS) don't directly use
PERF_RECORD_TIME_CONV for retriving TSC parameters.

I agree using PERF_RECORD_TIME_CONV for TSC parameter is better than
extending auxtrace info.  Will experiment for this.

> perf_read_tsc_conversion and perf_event__synth_time_conv are currently
> in arch/x86/util/tsc.c, but nothing in them is x86-specific and they could be
> moved somewhere more generic.

This is not true on the mainline kernel; these functions have been
moved into the file util/tsc.c.

Thanks for suggestions,
Leo