Messages in this thread | | | Subject | Re: [PATCH v2] xen/spinlock: Don't use pvqspinlock if only 1 vCPU | From | Boris Ostrovsky <> | Date | Thu, 19 Jul 2018 18:35:46 -0400 |
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On 07/19/2018 05:39 PM, 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. > > The xen_pvspin veriable is also turned off in this 1 vCPU case to > eliminate unneeded pvqspinlock initialization in xen_init_lock_cpu() > which is run after xen_init_spinlocks(). > > Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> --- > arch/x86/xen/spinlock.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c > index cd97a62..973f10e 100644 > --- a/arch/x86/xen/spinlock.c > +++ b/arch/x86/xen/spinlock.c > @@ -130,6 +130,10 @@ void xen_uninit_lock_cpu(int cpu) > void __init xen_init_spinlocks(void) > { > > + /* Don't need to use pvqspinlock code if there is only 1 vCPU. */ > + if (num_possible_cpus() == 1) > + xen_pvspin = false; > + > if (!xen_pvspin) { > printk(KERN_DEBUG "xen: PV spinlocks disabled\n"); > return;
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