Messages in this thread | | | Date | Tue, 14 Aug 2018 12:51:52 -0700 | From | Solio Sarabia <> | Subject | Time accounting difference under high IO interrupts |
| |
Under high IO activity (storage or network), the kernel is not accounting some cpu cycles, comparing sar vs emon (tool that accesses hw pmu directly). The difference is higher on cores that spend most time on idle state and are constantly waking up to handle interrupts. It happens even with fine IRQ time accounting enabled (CONFIG_IRQ_TIME_ACCOUNTING).
After playing with timer subsytem options (periodick ticks, idle tickless, full tickless), time and stats accounting, and jiffie values, the issue persists. Cycles lost are not accounted on other cores as 'extra' util. Example with linux 4.15.18 baremetal, xeon v4 broadwell, driving network traffic:
sar emon emon-sar intrs/sec core12 5.00 11.70 6.70 29,302 core17 19.07 23.16 4.09 17,345 core20 19.41 23.11 3.70 16,578
Based on how kernel accounts time: Do you have an idea why a high number of intrs affect time accounting?
Thanks, -Solio
| |