On Thu, Nov 06, 2014 at 04:51:58PM +0000, Pawel Moll wrote:
> Currently three clocks are implemented: CLOCK_REALITME = 0,
> CLOCK_MONOTONIC = 1 and CLOCK_MONOTONIC_RAW = 2. The clock field is
> 5 bits wide to allow for future extension to custom, non-POSIX clock
> sources(MAX_CLOCK for those is 16, see include/uapi/linux/time.h) like
> ARM CoreSight (hardware trace) timestamp generator.
> @@ -304,7 +305,16 @@ struct perf_event_attr {
> mmap2 : 1, /* include mmap with inode
> data */
> comm_exec : 1, /* flag comm events that
> are due to an exec */
> uevents : 1, /* allow uevents into the
> buffer */
> - __reserved_1 : 38;
> +
> + /*
> + * clock: one of the POSIX clock IDs:
> + *
> + * 0 - CLOCK_REALTIME
> + * 1 - CLOCK_MONOTONIC
> + * 4 - CLOCK_MONOTONIC_RAW
> + */
> + clock : 5, /* clock type */
> + __reserved_1 : 33;
>
> union {
> __u32 wakeup_events; /* wakeup every n events */
This would put a constraint on actually changing MAX_CLOCKS, are the
time people OK with that? Thomas, John?
I'm also not quite sure of using the >MAX_CLOCKS space for 'special'
clocks, preferably those would register themselves with the POSIX clock
interface.
> @@ -4631,6 +4637,24 @@ static void __perf_event_header__init_id(struct
> perf_event_header *header,
> data->cpu_entry.cpu = raw_smp_processor_id();
> data->cpu_entry.reserved = 0;
> }
> +
> + if (sample_type & PERF_SAMPLE_CLOCK) {
> + switch (event->attr.clock) {
> + case CLOCK_REALTIME:
> + data->clock = ktime_get_real_ns();
> + break;
> + case CLOCK_MONOTONIC:
> + data->clock = ktime_get_mono_fast_ns();
> + break;
> + case CLOCK_MONOTONIC_RAW:
> + data->clock = ktime_get_raw_ns();
> + break;
> + default:
> + data->clock = 0;
> + break;
> + }
> + }
> +
> }
This is broken. There is nothing stopping this from being called from
NMI context and only the MONO one is NMI safe.
Also, one would expect something like:
default: {
struct k_clock *kc = clockid_to_kclock(event->attr.clock);
struct timespec ts;
if (kc) {
kc->clock_get(event->attr.clock, &ts);
data->clock = ktime_to_ns(timespec_to_ktime(ts));
} else {
data->clock = 0;
}
}
Albeit preferably slightly less horrible -- of course, one would first
need to deal with the NMI issue.
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