On Fri, Aug 07, 2020 at 05:05:17PM -0600, Rob Herring wrote:
> x86 and arm64 can both support direct access of event counters in
> userspace. The access sequence is less than trivial and currently exists
> in perf test code (tools/perf/arch/x86/tests/rdpmc.c) with copies in
> projects such as PAPI and libpfm4.
>
> Patches to add arm64 userspace support are pending[1].
>
> For this RFC, looking for a yes, seems like a good idea, or no, go away we
> don't want this in libperf.
hi,
looks great!
I wanted to add this for very long time.. so yes, we want this ;-)
>
> TODO:
> - Handle userspace access not enabled.
> - Handle pmc_width and cap_user_time_short in read loop.
> - Move existing rdpmc test to libperf based test?
> - Abstract out rdtsc/rdpmc (currently only builds on x86 and need to add
> Arm versions)
all of them seem good, also please add test for perf_mmap__read_self
itself and update the doc/man
SNIP
> +{
> + struct perf_event_mmap_page *pc = map->base;
> + u32 seq, idx, time_mult = 0, time_shift = 0;
> + u64 count, cyc = 0, time_offset = 0, enabled, running, delta;
> +
> + /*
> + * Check if event was unmapped due to a POLLHUP/POLLERR.
> + */
> + if (!refcount_read(&map->refcnt))
> + return ~0;
> +
> + do {
> + seq = pc->lock;
> + barrier();
> +
> + enabled = pc->time_enabled;
> + running = pc->time_running;
> +
> + if (enabled != running) {
should you check pc->cap_usr_time in here?
> + cyc = rdtsc();
> + time_mult = pc->time_mult;
> + time_shift = pc->time_shift;
> + time_offset = pc->time_offset;
> + }
> +
> + idx = pc->index;
> + count = pc->offset;
> + if (idx)
and pc->cap_user_rdpmc in here?
ok, it's probably in the TODO
thanks,
jirka
