| Message ID | 1347046931.7332.51.camel@oc2024037011.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
> > signed-off-by: Andrew Theurer <habanero@linux.vnet.ibm.com> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index fbf1fd0..c767915 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4844,6 +4844,9 @@ bool __sched yield_to(struct task_struct *p, bool > preempt) > > again: > p_rq = task_rq(p); > + if (task_running(p_rq, p) || p->state || !(p_rq->curr->flags & > PF_VCPU)) { > + goto out_no_unlock; > + } > double_rq_lock(rq, p_rq); > while (task_rq(p) != p_rq) { > double_rq_unlock(rq, p_rq); > @@ -4856,8 +4859,6 @@ again: > if (curr->sched_class != p->sched_class) > goto out; > > - if (task_running(p_rq, p) || p->state) > - goto out; Is it possible that by this time the current thread takes double rq lock, thread p could actually be running? i.e is there merit to keep this check around even with your similar check above? > > yielded = curr->sched_class->yield_to_task(rq, p, preempt); > if (yielded) { > @@ -4879,6 +4880,7 @@ again: > > out: > double_rq_unlock(rq, p_rq); > +out_no_unlock: > local_irq_restore(flags); > > if (yielded) > >
On Sat, 2012-09-08 at 14:13 +0530, Srikar Dronamraju wrote: > > > > signed-off-by: Andrew Theurer <habanero@linux.vnet.ibm.com> > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index fbf1fd0..c767915 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -4844,6 +4844,9 @@ bool __sched yield_to(struct task_struct *p, bool > > preempt) > > > > again: > > p_rq = task_rq(p); > > + if (task_running(p_rq, p) || p->state || !(p_rq->curr->flags & > > PF_VCPU)) { > > + goto out_no_unlock; > > + } > > double_rq_lock(rq, p_rq); > > while (task_rq(p) != p_rq) { > > double_rq_unlock(rq, p_rq); > > @@ -4856,8 +4859,6 @@ again: > > if (curr->sched_class != p->sched_class) > > goto out; > > > > - if (task_running(p_rq, p) || p->state) > > - goto out; > > Is it possible that by this time the current thread takes double rq > lock, thread p could actually be running? i.e is there merit to keep > this check around even with your similar check above? I think that's a good idea. I'll add that back in. > > > > > yielded = curr->sched_class->yield_to_task(rq, p, preempt); > > if (yielded) { > > @@ -4879,6 +4880,7 @@ again: > > > > out: > > double_rq_unlock(rq, p_rq); > > +out_no_unlock: > > local_irq_restore(flags); > > > > if (yielded) > > > > > -Andrew Theurer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 09/08/2012 01:12 AM, Andrew Theurer wrote: > On Fri, 2012-09-07 at 23:36 +0530, Raghavendra K T wrote: >> CCing PeterZ also. >> >> On 09/07/2012 06:41 PM, Andrew Theurer wrote: >>> I have noticed recently that PLE/yield_to() is still not that scalable >>> for really large guests, sometimes even with no CPU over-commit. I have >>> a small change that make a very big difference. [...] >> We are indeed avoiding CPUS in guest mode when we check >> task->flags& PF_VCPU in vcpu_on_spin path. Doesn't that suffice? > My understanding is that it checks if the candidate vcpu task is in > guest mode (let's call this vcpu g1vcpuN), and that vcpu will not be a > target to yield to if it is already in guest mode. I am concerned about > a different vcpu, possibly from a different VM (let's call it g2vcpuN), > but it also located on the same runqueue as g1vcpuN -and- running. That > vcpu, g2vcpuN, may also be doing a directed yield, and it may already be > holding the rq lock. Or it could be in guest mode. If it is in guest > mode, then let's still target this rq, and try to yield to g1vcpuN. > However, if g2vcpuN is not in guest mode, then don't bother trying. - If a non vcpu task was currently running, this change can ignore request to yield to a target vcpu. The target vcpu could be the most eligible vcpu causing other vcpus to do ple exits. Is it possible to modify the check to deal with only vcpu tasks? - Should we use p_rq->cfs_rq->skip instead to let us know that some yield was active at this time? - Cpu 1 cpu2 cpu3 a1 a2 a3 b1 b2 b3 c2(yield target of a1) c3(yield target of a2) If vcpu a1 is doing directed yield to vcpu c2; current vcpu a2 on target cpu is also doing a directed yield(to some vcpu c3). Then this change will only allow vcpu a2 will do a schedule() to b2 (if a2 -> c3 yield is successful). Do we miss yielding to a vcpu c2? a1 might not find a suitable vcpu to yield and might go back to spinning. Is my understanding correct? > Patch include below. > > Here's the new, v2 result with the previous two: > > 10 VMs, 16-way each, all running dbench (2x cpu over-commit) > throughput +/- stddev > ----- ----- > ple on: 2552 +/- .70% > ple on: w/fixv1: 4621 +/- 2.12% (81% improvement) > ple on: w/fixv2: 6115* (139% improvement) > The numbers look great. > [*] I do not have stdev yet because all 10 runs are not complete > > for v1 to v2, host CPU dropped from 60% to 50%. Time in spin_lock() is > also dropping: > [...] > > So this seems to be working. However I wonder just how far we can take > this. Ideally we need to be in<3-4% in host for PLE work, like I > observe for the 8-way VMs. We are still way off. > > -Andrew > > > signed-off-by: Andrew Theurer<habanero@linux.vnet.ibm.com> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index fbf1fd0..c767915 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4844,6 +4844,9 @@ bool __sched yield_to(struct task_struct *p, bool > preempt) > > again: > p_rq = task_rq(p); > + if (task_running(p_rq, p) || p->state || !(p_rq->curr->flags& > PF_VCPU)) { While we are checking the flags of p_rq->curr task, the task p can migrate to some other runqueue. In this case will we miss yielding to the most eligible vcpu? > + goto out_no_unlock; > + } Nit: We dont need parenthesis above. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index fbf1fd0..c767915 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4844,6 +4844,9 @@ bool __sched yield_to(struct task_struct *p, bool preempt) again: p_rq = task_rq(p); + if (task_running(p_rq, p) || p->state || !(p_rq->curr->flags & PF_VCPU)) { + goto out_no_unlock; + } double_rq_lock(rq, p_rq);