Re: [PATCH bpf-next v2 07/26] rqspinlock: Add support for timeouts

Peter Zijlstra
2025-02-10T09:56:13Z

On Thu, Feb 06, 2025 at 02:54:15AM -0800, Kumar Kartikeya Dwivedi wrote:
> @@ -68,6 +71,44 @@
>
> #include "mcs_spinlock.h"
>
> +struct rqspinlock_timeout {
> + u64 timeout_end;
> + u64 duration;
> + u16 spin;
> +};
> +
> +static noinline int check_timeout(struct rqspinlock_timeout *ts)
> +{
> + u64 time = ktime_get_mono_fast_ns();

This is only sane if you have a TSC clocksource. If you ever manage to
hit the HPET fallback, you're *really* sad.

> +
> + if (!ts->timeout_end) {
> + ts->timeout_end = time + ts->duration;
> + return 0;
> + }
> +
> + if (time > ts->timeout_end)
> + return -ETIMEDOUT;
> +
> + return 0;
> +}
> +
> +#define RES_CHECK_TIMEOUT(ts, ret) \
> + ({ \
> + if (!(ts).spin++) \
> + (ret) = check_timeout(&(ts)); \
> + (ret); \
> + })