Re: [PATCH 1/6] delayacct: Use sched_clock()

[Johannes Weiner]

On Wed, May 05, 2021 at 12:59:41PM +0200, Peter Zijlstra wrote:
> @@ -42,10 +42,9 @@ void __delayacct_tsk_init(struct task_st
>   * Finish delay accounting for a statistic using its timestamps (@start),
>   * accumalator (@total) and @count
>   */
> -static void delayacct_end(raw_spinlock_t *lock, u64 *start, u64 *total,
> -			  u32 *count)
> +static void delayacct_end(raw_spinlock_t *lock, u64 *start, u64 *total, u32 *count)
>  {
> -	s64 ns = ktime_get_ns() - *start;
> +	s64 ns = local_clock() - *start;

I don't think this is safe. These time sections that have preemption
and migration enabled and so might span multiple CPUs. local_clock()
could end up behind *start, AFAICS.