On Fri, May 08, 2020 at 04:49:04PM +0530, Parth Shah wrote: > Hi Pavan, > > On 5/8/20 2:06 PM, Pavan Kondeti wrote: > > On Thu, May 07, 2020 at 07:07:22PM +0530, Parth Shah wrote: > >> Restrict the call to deeper idle states when the given CPU has been set for > >> the least latency requirements > >> > >> Signed-off-by: Parth Shah <[email protected]> > >> --- > >> kernel/sched/idle.c | 3 ++- > >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > >> index b743bf38f08f..85d72a6e2521 100644 > >> --- a/kernel/sched/idle.c > >> +++ b/kernel/sched/idle.c > >> @@ -262,7 +262,8 @@ static void do_idle(void) > >> * broadcast device expired for us, we don't want to go deep > >> * idle as we know that the IPI is going to arrive right away. > >> */ > >> - if (cpu_idle_force_poll || tick_check_broadcast_expired()) { > >> + if (cpu_idle_force_poll || tick_check_broadcast_expired() || > >> + per_cpu(nr_lat_sensitive, cpu)) { > >> tick_nohz_idle_restart_tick(); > >> cpu_idle_poll(); > >> } else { > >> -- > >> 2.17.2 > >> > > > > Since nr_lat_sensitive updates can happen remotely (when a latency sensitive > > task becomes non-latency sensitive task), we may need to add this condition > > in cpu_idle_poll() as well. > > > > Right. but if the CPU is running idle_task then it will again come back to > do_idle and read the refcount. Its a penalty in power-saving for 1 > do_idle() loop but it is difficult to put up checks for any change in > latency_nice value. >
Yes, when the CPU exits to serve an interrupt, we note the change in latency task count and enter C-state. I asked this because all checks that are present here are also present in cpu_idle_poll(). Thanks, Pavan -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
