Re: locking/csd-lock: Switch from sched_clock() to ktime_get_mono_fast_ns()

[Rik van Riel]

On Wed, 2024-10-09 at 10:57 -0700, Paul E. McKenney wrote:
> Currently, the CONFIG_CSD_LOCK_WAIT_DEBUG code uses sched_clock()
> to check for excessive CSD-lock wait times.  This works, but does not
> guarantee monotonic timestamps.  Therefore, switch from sched_clock()
> to ktime_get_mono_fast_ns(), which does guarantee monotonic
> timestamps,
> at least in the absence of calls from NMI handlers, which are not
> involved
> in this code path.
> 
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Neeraj Upadhyay <neeraj.upadhyay@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxxx>
> Cc: Leonardo Bras <leobras@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>

The functional change here is that sched_clock() uses rdtsc(),
while ktime_get_mono_fast_ns() uses rdtsc_ordered().

I don't know if sched_clock() should also be using rdtsc_ordered().

Reviewed-by: Rik van Riel <riel@xxxxxxxxxxx>


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