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xen/spinlock: Don't use pvqspinlock if only 1 vCPU 

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>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
This commit is contained in:
Waiman Long 2018-07-19 17:39:57 -04:00 committed by Boris Ostrovsky
parent bf8dc55b13
commit 47b428d14f
1 changed files with 4 additions and 0 deletions
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4
arch/x86/xen/spinlock.c
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@ -130,6 +130,10 @@ PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
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;