[PATCH v2 0/4] implement vcpu preempted check
waiman.long at hpe.com
Wed Jul 13 04:16:30 AEST 2016
On 07/12/2016 12:16 AM, Juergen Gross wrote:
> On 11/07/16 17:10, Waiman Long wrote:
>> On 07/06/2016 02:52 AM, Peter Zijlstra wrote:
>>> On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote:
>>>> change fomr v1:
>>>> a simplier definition of default vcpu_is_preempted
>>>> skip mahcine type check on ppc, and add config. remove dedicated
>>>> add one patch to drop overload of rwsem_spin_on_owner and
>>>> add more comments
>>>> thanks boqun and Peter's suggestion.
>>>> This patch set aims to fix lock holder preemption issues.
>>>> perf record -a perf bench sched messaging -g 400 -p&& perf report
>>>> 18.09% sched-messaging [kernel.vmlinux] [k] osq_lock
>>>> 12.28% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner
>>>> 5.27% sched-messaging [kernel.vmlinux] [k] mutex_unlock
>>>> 3.89% sched-messaging [kernel.vmlinux] [k] wait_consider_task
>>>> 3.64% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq
>>>> 3.41% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner.is
>>>> 2.49% sched-messaging [kernel.vmlinux] [k] system_call
>>>> We introduce interface bool vcpu_is_preempted(int cpu) and use it in
>>>> some spin
>>>> loops of osq_lock, rwsem_spin_on_owner and mutex_spin_on_owner.
>>>> These spin_on_onwer variant also cause rcu stall before we apply this
>>>> patch set
>>> Paolo, could you help out with an (x86) KVM interface for this?
>>> Waiman, could you see if you can utilize this to get rid of the
>>> SPIN_THRESHOLD in qspinlock_paravirt?
>> That API is certainly useful to make the paravirt spinlock perform
>> better. However, I am not sure if we can completely get rid of the
>> SPIN_THRESHOLD at this point. It is not just the kvm, the xen code need
>> to be modified as well.
> This should be rather easy. The relevant information is included in the
> runstate data mapped into kernel memory. I can provide a patch for Xen
> if needed.
Thanks for the offering. We will wait until Xinhui's patch comes through
before working on the next step.
As for the elimination of SPIN_THRESHOLD, the queue head may not always
have the right CPU number of the lock holder. So I don't think we can
eliminate that for the queue head spinning. I think we can eliminates
the SPIN_THRESHOLD spinning for the other queue node vCPUs.
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