On 2/25/19 3:07 PM, Stanislav Fomichev wrote:
>> +#define BPF_PROG_RUN(prog, ctx) ({ \
>> + u32 ret; \
>> + cant_sleep(); \
>> + if (static_branch_unlikely(&bpf_stats_enabled_key)) { \
>> + struct bpf_prog_stats *stats; \
>> + u64 start = sched_clock(); \
> QQ: why sched_clock() and not, for example, ktime_get_ns() which we do
> in the bpf_test_run()? Or even why not local_clock?
> I'm just wondering what king of trade off we are doing here
> regarding precision vs run time cost.
I'm making this decision based on documentation:
Documentation/timers/timekeeping.txt
"Compared to clock sources, sched_clock() has to be very fast: it is
called much more often, especially by the scheduler. If you have to do
trade-offs between accuracy compared to the clock source, you may
sacrifice accuracy for speed in sched_clock()."
