From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3tLMDY0XVHzDvy9 for ; Sat, 19 Nov 2016 15:23:25 +1100 (AEDT) Date: Sat, 19 Nov 2016 14:53:43 +1100 From: Paul Mackerras To: "Aneesh Kumar K.V" Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@ozlabs.org Subject: Re: [PATCH 10/13] KVM: PPC: Book3S HV: Use msgsnd for IPIs to other cores on POWER9 Message-ID: <20161119035343.GA29462@fergus.ozlabs.ibm.com> References: <1479454122-26994-1-git-send-email-paulus@ozlabs.org> <1479454122-26994-11-git-send-email-paulus@ozlabs.org> <87vavkn8ua.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <87vavkn8ua.fsf@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, Nov 18, 2016 at 08:17:25PM +0530, Aneesh Kumar K.V wrote: > Paul Mackerras writes: > > > On POWER9, the msgsnd instruction is able to send interrupts to > > other cores, as well as other threads on the local core. Since > > msgsnd is generally simpler and faster than sending an IPI via the > > XICS, we use msgsnd for all IPIs sent by KVM on POWER9. > > > > Signed-off-by: Paul Mackerras > > --- > > arch/powerpc/kvm/book3s_hv.c | 11 ++++++++++- > > arch/powerpc/kvm/book3s_hv_builtin.c | 10 ++++++++-- > > 2 files changed, 18 insertions(+), 3 deletions(-) > > [...] > > diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c > > index 0c84d6b..37ed045 100644 > > --- a/arch/powerpc/kvm/book3s_hv_builtin.c > > +++ b/arch/powerpc/kvm/book3s_hv_builtin.c > > @@ -205,12 +205,18 @@ static inline void rm_writeb(unsigned long paddr, u8 val) > > void kvmhv_rm_send_ipi(int cpu) > > { > > unsigned long xics_phys; > > + unsigned long msg = PPC_DBELL_TYPE(PPC_DBELL_SERVER); > > > > - /* On POWER8 for IPIs to threads in the same core, use msgsnd */ > > + /* On POWER9 we can use msgsnd for any destination cpu. */ > > + if (cpu_has_feature(CPU_FTR_ARCH_300)) { > > + msg |= get_hard_smp_processor_id(cpu); > > + __asm__ __volatile__ (PPC_MSGSND(%0) : : "r" (msg)); > > + return; > > Do we need a "sync" there before msgsnd ? The comment just above this function says: /* * Send an interrupt or message to another CPU. * This can only be called in real mode. * The caller needs to include any barrier needed to order writes * to memory vs. the IPI/message. */ so no. In fact all of its callers do smp_mb() before calling it. (And no we don't want to move the smp_mb() into kvmhv_rm_send_ipi(); see kvmhv_interrupt_vcore() for why.) Paul.