Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls

Thomas Gleixner
2021-11-26T21:13:20Z

On Wed, Nov 24 2021 at 22:19, Peter Zijlstra wrote:
> On Mon, Nov 22, 2021 at 01:13:24PM -0800, Peter Oskolkov wrote:
>
>> + * Timestamp: a 46-bit CLOCK_MONOTONIC timestamp, at 16ns resolution.
>
>> +static int umcg_update_state(u64 __user *state_ts, u64 *expected, u64 desired,
>> + bool may_fault)
>> +{
>> + u64 curr_ts = (*expected) >> (64 - UMCG_STATE_TIMESTAMP_BITS);
>> + u64 next_ts = ktime_get_ns() >> UMCG_STATE_TIMESTAMP_GRANULARITY;
>
> I'm still very hesitant to use ktime (fear the HPET); but I suppose it
> makes sense to use a time base that's accessible to userspace. Was
> MONOTONIC_RAW considered?

MONOTONIC_RAW is not really useful as you can't sleep on it and it won't
solve the HPET crap either.

Thanks,

tglx