On Fri, Mar 03, 2017 at 01:41:59PM -0600, Julia Cartwright wrote:
> On Thu, Mar 02, 2017 at 03:23:02AM +0000, Patel, Vedang wrote:
[..]
> > Case 1:
> > TASK CPU TIMESTAMP EVENT
> > cyclictest-2351 [003] 7773.130964: hrtimer_start: hrtimer=0xffff88046b098828 function=posix_timer_fn/0x0 expires=7767043047952 softexpires=7767043047952
> > cyclictest-2351 [003] 7773.130978: sched_switch: cyclictest:2351 [19] S ==> ktimersoftd/3:36 [98]
> > ktimersoftd/3-36 [003] 7773.130992: sched_switch: ktimersoftd/3:36 [98] R ==> cyclictest:2351 [19]
> > cyclictest-2351 [003] 7773.131003: sched_switch: cyclictest:2351 [19] D ==> ktimersoftd/3:36 [19] <--- cyclictest is in TASK_UNINTERRUPTIBLE state.
> > ktimersoftd/3-36 [003] 7773.131006: signal_generate: sig=14 errno=0 code=131070 comm=cyclictest pid=2351 grp=0 res=0
> > ktimersoftd/3-36 [003] 7773.131018: sched_switch: ktimersoftd/3:36 [98] R ==> cyclictest:2351 [19]
> > cyclictest-2351 [003] 7773.131031: sched_switch: cyclictest:2351 [19] D ==> ktimersoftd/3:36 [19]
> > ktimersoftd/3-36 [003] 7773.131046: sched_switch: ktimersoftd/3:36 [98] R ==> cyclictest:2351 [19]
>
> This ktimersoftd -> cyclictest -> ktimersoftd -> cyclictest "bounce" is
> a result of how the signal completion code for the posix itimers is
> done.
>
> [ktimersoftd] [cyclictest]
> lock task->sighand
> set pending signal
> signal_wake_up(task) --->
> lock task->sighand (*blocked*, state D)
> <---
> trace signal_generate
> unlock task->sighand
> --->
> while (!pending signal)
> unlock task->sighand
> wait for signal
> lock task->sighand
> unlock task->sighand
A corrected diagram below (same codepaths, layed out differently):
[ktimersoftd] [cyclictest]
lock task->sighand
while (!pending signal) {
unlock task->sighand
wait for signal (state S)
... after interval ...
lock task->sighand
set pending signal
signal_wake_up(task) ---> (woken, state R)
lock task->sighand (*blocked*, state D)
<---
trace signal_generate
unlock task->sighand
---> }
unlock task->sighand
...
Julia
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