lkml.org 
[lkml]   [2018]   [Jul]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH v2] xen/spinlock: Don't use pvqspinlock if only 1 vCPU
On Thu, 19 Jul 2018, 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().

Wouldn't kvm also want this?

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index a37bda38d205..95aceb692010 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -457,7 +457,8 @@ static void __init sev_map_percpu_data(void)
static void __init kvm_smp_prepare_cpus(unsigned int max_cpus)
{
native_smp_prepare_cpus(max_cpus);
- if (kvm_para_has_hint(KVM_HINTS_REALTIME))
+ if (num_possible_cpus() == 1 ||
+ kvm_para_has_hint(KVM_HINTS_REALTIME))
static_branch_disable(&virt_spin_lock_key);
}
\
 
 \ /
  Last update: 2018-07-19 23:56    [W:0.084 / U:0.476 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site