From: Paolo Bonzini <pbonzini@redhat.com>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Yang Zhang" <yang.zhang.wz@gmail.com>,
"feng wu" <feng.wu@intel.com>,
mst@redhat.com
Subject: Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry
Date: Fri, 14 Oct 2016 14:56:38 -0400 (EDT) [thread overview]
Message-ID: <770436977.3704467.1476471398385.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <4B0C832B-BB75-40BD-85A9-9DC84DEB44E2@gmail.com>
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index 23b99f305382..63a442aefc12 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -342,9 +342,11 @@ void __kvm_apic_update_irr(u32 *pir, void *regs)
> > u32 i, pir_val;
> >
> > for (i = 0; i <= 7; i++) {
> > - pir_val = xchg(&pir[i], 0);
> > - if (pir_val)
> > + pir_val = READ_ONCE(pir[i]);
>
> Out of curiosity, do you really need this READ_ONCE?
The answer can only be "depends on the compiler's whims". :)
If you think of READ_ONCE as a C11 relaxed atomic load, then yes.
Paolo
next prev parent reply other threads:[~2016-10-14 18:56 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-14 18:21 [PATCH 0/5] KVM: x86: cleanup and minimal speedup for APICv Paolo Bonzini
2016-10-14 18:21 ` [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry Paolo Bonzini
2016-10-14 18:50 ` Nadav Amit
2016-10-14 18:56 ` Paolo Bonzini [this message]
2016-10-14 19:44 ` Nadav Amit
2016-10-15 7:47 ` Paolo Bonzini
2016-10-16 2:29 ` Michael S. Tsirkin
2016-10-19 11:45 ` Paul E. McKenney
2016-10-26 21:50 ` Michael S. Tsirkin
2016-10-16 3:21 ` Michael S. Tsirkin
2016-10-17 11:07 ` Paolo Bonzini
2016-10-26 19:53 ` Radim Krčmář
2016-10-26 21:42 ` Michael S. Tsirkin
2016-10-27 16:44 ` Radim Krčmář
2016-10-27 16:51 ` Michael S. Tsirkin
2016-10-27 17:06 ` Radim Krčmář
2016-10-28 9:39 ` Paolo Bonzini
2016-10-28 22:04 ` Michael S. Tsirkin
2016-10-14 18:21 ` [PATCH 2/5] KVM: x86: do not scan IRR twice " Paolo Bonzini
2016-10-18 6:04 ` Wanpeng Li
2016-10-26 19:59 ` Radim Krčmář
2016-11-03 13:30 ` Paolo Bonzini
2016-11-03 13:53 ` Michael S. Tsirkin
2016-11-03 16:01 ` Paolo Bonzini
2016-11-03 15:03 ` Radim Krčmář
2016-11-03 16:00 ` Paolo Bonzini
2016-11-03 18:07 ` Radim Krčmář
2016-11-03 18:18 ` Paolo Bonzini
2016-11-03 18:29 ` Radim Krčmář
2016-11-03 20:16 ` Radim Krčmář
2016-11-04 9:38 ` Paolo Bonzini
2016-10-14 18:21 ` [PATCH 3/5] KVM: x86: do not use KVM_REQ_EVENT for APICv interrupt injection Paolo Bonzini
2016-10-26 20:05 ` Radim Krčmář
2016-10-14 18:21 ` [PATCH 4/5] KVM: x86: remove unnecessary sync_pir_to_irr Paolo Bonzini
2016-10-26 20:28 ` Radim Krčmář
2016-10-14 18:21 ` [PATCH 5/5] KVM: vmx: clear pending interrupts on KVM_SET_LAPIC Paolo Bonzini
2016-10-26 20:08 ` Radim Krčmář
2016-10-26 21:52 ` [PATCH 0/5] KVM: x86: cleanup and minimal speedup for APICv Michael S. Tsirkin
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