Re: [PATCH] tick/nohz: Avoid unused timekeeping_max_deferment() calls

[Usama Arif <usama.arif@linux.dev>]

On 18/09/2026 14:33, Usama Arif wrote:
> tick_nohz_next_event() limits a CPU's sleep interval to the maximum
> deferment supported by the current clocksource when that CPU owns the
> do_timer() duty. If the duty is unassigned, the limit also applies when
> the CPU's TS_FLAG_DO_TIMER_LAST flag is set.
> 
> After the early timer checks, the function currently reads the maximum
> deferment unconditionally. It then replaces the result with KTIME_MAX
> unless one of the two conditions above applies.
> 
> timekeeping_max_deferment() performs a seqcount-protected read of the
> shared timekeeper and follows its clocksource pointer. Check the do_timer
> state first and avoid this work when the result would be discarded. This
> leaves the resulting expiry unchanged and reduces accesses to timekeeper
> data that is modified regularly.
> 
> On x86-64 this removes 18-20 dynamically executed instructions, including
> the call, from the common non-owner path when the seqcount does not retry.
> 
> Signed-off-by: Usama Arif <usama.arif@linux.dev>
> ---
> v1 -> v2:
> - Remove the unnecessary comment and delta variable (Frederic Weisbecker).
> ---
>  kernel/time/tick-sched.c | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
Sorry about the noise, please ignore, copied the wrong list of people to send to.
The correct list is [1]

[1] https://lore.kernel.org/all/20260918133408.2834751-1-usama.arif@linux.dev/