Messages in this thread | | | Subject | Re: [PATCH] xen/spinlock: Don't use pvqspinlock if only 1 vCPU | From | Boris Ostrovsky <> | Date | Thu, 19 Jul 2018 15:18:58 -0400 |
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On 07/19/2018 09:48 AM, Waiman Long wrote: > On a VM with only 1 vCPU, the locking fast paths will always be > successful. In this case, there is no need to use the the PV qspinlock > code which has higher overhead on the unlock side than the native > qspinlock code. > > Signed-off-by: Waiman Long <longman@redhat.com> > --- > arch/x86/xen/spinlock.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c > index cd97a62..38f47ae 100644 > --- a/arch/x86/xen/spinlock.c > +++ b/arch/x86/xen/spinlock.c > @@ -130,7 +130,8 @@ void xen_uninit_lock_cpu(int cpu) > void __init xen_init_spinlocks(void) > { > > - if (!xen_pvspin) { > + /* Don't need to use pvqspinlock code if there is only 1 vCPU. */ > + if (!xen_pvspin || num_possible_cpus() == 1) { > printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); > return; > }
I think we need to set xen_pvspin to false for such configurations. Notice that xen_init_lock_cpu() will try to perform some additional pvspinlock initializations.
-boris
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