On Fri, Jun 28, 2019 at 08:43:12AM +0800, Wanpeng Li wrote: > From: Wanpeng Li <[email protected]> > > On a machine, cpu 0 is used for housekeeping, the other 39 cpus in the > same socket are in nohz_full mode. We can observe huge time burn in the > loop for seaching nearest busy housekeeper cpu by ftrace. > > 2) | get_nohz_timer_target() { > 2) 0.240 us | housekeeping_test_cpu(); > 2) 0.458 us | housekeeping_test_cpu(); > > ... > > 2) 0.292 us | housekeeping_test_cpu(); > 2) 0.240 us | housekeeping_test_cpu(); > 2) 0.227 us | housekeeping_any_cpu(); > 2) + 43.460 us | } > > This patch optimizes the searching logic by finding a nearest housekeeper > cpu in the housekeeping cpumask, it can minimize the worst searching time > from ~44us to < 10us in my testing. In addition, the last iterated busy > housekeeper can become a random candidate while current CPU is a better > fallback if it is a housekeeper. > > Cc: Ingo Molnar <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Frederic Weisbecker <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Signed-off-by: Wanpeng Li <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]> Thanks!
