Messages in this thread | | | Date | Fri, 12 Feb 2016 16:22:29 -0500 | From | Waiman Long <> | Subject | Re: [PATCH v2 4/4] sched/fair: Abort wakeup when task is no longer in a sleeping state |
| |
On 02/12/2016 03:18 PM, Peter Zijlstra wrote: > On Fri, Feb 12, 2016 at 12:32:15PM -0500, Waiman Long wrote: >> When a task prepares to sleep and then aborts it somehow, there is >> a small chance that a waker may be spinning on the on_cpu flag of >> that task waiting for the flag to turn off before doing the wakeup >> operation. It may keep on spinning for a long time until that task >> actually sleeps leading to spurious wakeup. >> >> This patch adds code to detect the change in task state and abort >> the wakeup operation, when appropriate, to free up the waker's cpu >> to do other useful works. >> >> Signed-off-by: Waiman Long<Waiman.Long@hp.com> >> --- >> kernel/sched/core.c | 9 ++++++++- >> 1 files changed, 8 insertions(+), 1 deletions(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 7e548bd..e4b6e84 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -2075,8 +2075,15 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) >> * >> * This ensures that tasks getting woken will be fully ordered against >> * their previous state and preserve Program Order. >> + * >> + * If the owning cpu decides not to sleep after all by changing back >> + * its task state, we can return immediately. >> */ >> - smp_cond_acquire(!p->on_cpu); >> + smp_cond_acquire(!p->on_cpu || !(p->state& state)); >> + if (!(p->state& state)) { >> + success = 0; >> + goto out; >> + } > This doesn't make sense, if we managed to get here, p->on_rq must be > false, which means the other side is already in the middle of > schedule(). Yes, you are right. It is my bad that I miss the on_rq check earlier. Just scrap the last patch.
Sorry for that:-[ Longman
| |