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

Peter Zijlstra
2021-11-24T21:19:44Z

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?