Messages in this thread | | | From | "Doug Smythies" <> | Subject | RE: [RFT][PATCH v7 6/8] sched: idle: Select idle state before stopping the tick | Date | Wed, 28 Mar 2018 13:41:35 -0700 |
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On 2018.03.28 08:15 Thomas Ilsche wrote: > On 2018-03-28 12:56, Rafael J. Wysocki wrote: >> On Wed, Mar 28, 2018 at 12:37 PM, Rafael J. Wysocki <rafael@kernel.org> wrote: >>> On Wed, Mar 28, 2018 at 10:38 AM, Thomas Ilsche >>> <thomas.ilsche@tu-dresden.de> wrote: >>>> On 2018-03-28 10:13, Rafael J. Wysocki wrote: >>>>> >> >> [cut] >> >>> >>> So I do >>> >>> $ for cpu in 0 1 2 3; do taskset -c $cpu sh -c 'while true; do usleep >>> 500; done' & done >>> >>> which is a shell kind of imitation of the above and I cannot see this >>> issue at all. >>> >>> I count the number of times data->next_timer_us in menu_select() is >>> greater than TICK_USEC and while this "workload" is running, that >>> number is exactly 0. >>> >>> I'll try with a C program still. >> >> And with a C program I see data->next_timer_us greater than TICK_USEC >> while it is running, so let me dig deeper. >> > > I can confirm that a shell-loop behaves differently like you describe. > Even if it's just a shell-loop calling "main{usleep(500);}" binary.
I normally use the C program method. The timer there returns with the need_sched() flag set.
I do not seem to have usleep on my system, but when using sleep in a shell loop, the timer returns without the need_resched() flag set.
Most of my test results involving varying the value of POLL_IDLE_COUNT are total garbage, because I was using the C program method, and thus exiting the poll_idle loop based on the need_resched() flag and not the POLL_IDLE_COUNT setting.
I don't know if I can re-do the work, because I do not have a good way to get my system to use Idle State 0 with any real workflow, and I seem to get into side effect issues when I disable other idle states to force more use of idle state 0.
... Doug
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