On 11/07/16 17:10, Waiman Long wrote:

On 07/06/2016 02:52 AM, Peter Zijlstra wrote:

quoted

On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote:

quoted

change fomr v1:
    a simplier definition of default vcpu_is_preempted
    skip mahcine type check on ppc, and add config. remove dedicated
macro.
    add one patch to drop overload of rwsem_spin_on_owner and
mutex_spin_on_owner.
    add more comments
    thanks boqun and Peter's suggestion.

This patch set aims to fix lock holder preemption issues.

test-case:
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.


Juergen