On Wed, 12 Jun 2019, Dmitry Safonov wrote: > From: Andrei Vagin <avagin@xxxxxxxxx> > > After performance testing VDSO patches a noticeable 20% regression was > found on gettime_perf selftest with a cold cache. > As it turns to be, before time namespaces introduction, VDSO functions > were quite aligned to cache lines, but adding a new code to adjust > timens offset inside namespace created a small shift and vdso functions > become unaligned on cache lines. > > Add align to vdso functions with gcc option to fix performance drop. > > Coping the resulting numbers from cover letter: > > Hot CPU cache (more gettime_perf.c cycles - the better): > | before | CONFIG_TIME_NS=n | host | inside timens > --------|------------|------------------|-------------|------------- > cycles | 139887013 | 139453003 | 139899785 | 128792458 > diff (%)| 100 | 99.7 | 100 | 92 Why is CONFIG_TIME_NS=n behaving worse than current mainline and worse than 'host' mode? > Cold cache (lesser tsc per gettime_perf_cold.c cycle - the better): > | before | CONFIG_TIME_NS=n | host | inside timens > --------|------------|------------------|-------------|------------- > tsc | 6748 | 6718 | 6862 | 12682 > diff (%)| 100 | 99.6 | 101.7 | 188 Weird, now CONFIG_TIME_NS=n is better than current mainline and 'host' mode drops. Either I'm misreading the numbers or missing something or I'm just confused as usual :) Thanks, tglx
