Commit 47b428d1 authored Jul 19, 2018 by Waiman Long Committed by Boris Ostrovsky Jul 26, 2018

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>

parent bf8dc55b

arch/x86/xen/spinlock.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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;

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