On 1/29/2024 3:48 PM, Uladzislau Rezki wrote: > On Mon, Jan 29, 2024 at 05:47:39PM +0000, Joel Fernandes wrote: >> Hi Guys, >> Something caught my eye in [1] which a colleague pointed me to >> - CONFIG_HZ=1000 : 14866.05 bogo ops/s >> - CONFIG_HZ=1000+nohz_full : 18505.52 bogo ops/s >> >> The test in concern is: >> stress-ng --matrix $(getconf _NPROCESSORS_ONLN) --timeout 5m --metrics-brief >> >> which is a CPU intensive test. >> >> Any thoughts on what else can attribute a 30% performance increase >> versus non-nohz_full ? (Confession: No idea if the baseline is >> nohz_idle or no nohz at all). If it is 30%, I may want to evaluate >> nohz_full on some of our limited-CPU devices :) >> > Timer overhead and its scheduler-callback? Yes, quite possible. > If i do not miss something > the NO_HZ_FULL will disable the timer if there is only one task on CPU > so that running task benefits from not being interrupted thus gets more > CPU time. Yes, that's right. I believe it is well known that HPC-type of workloads benefit from FULL, however it has led to want to try it out for constrained system as well where CPU cycles are a premium, especially if the improvement is like what the report suggests (give or take the concerns/questions Paul raised). Thanks, - Joel
