From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: MMU: Inform users of mmio generation wraparound Date: Thu, 20 Jun 2013 14:35:36 +0200 Message-ID: <51C2F718.1010500@redhat.com> References: <20130620175914.4e4f9eb3.yoshikawa_takuya_b1@lab.ntt.co.jp> <51C2E0AA.7060404@redhat.com> <20130620114504.GG5832@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Takuya Yoshikawa , kvm@vger.kernel.org, xiaoguangrong@linux.vnet.ibm.com To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:6967 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757442Ab3FTMf7 (ORCPT ); Thu, 20 Jun 2013 08:35:59 -0400 In-Reply-To: <20130620114504.GG5832@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Il 20/06/2013 13:45, Gleb Natapov ha scritto: > On Thu, Jun 20, 2013 at 12:59:54PM +0200, Paolo Bonzini wrote: >> Il 20/06/2013 10:59, Takuya Yoshikawa ha scritto: >>> Without this information, users will just see unexpected performance >>> problems and there is little chance we will get good reports from them: >>> note that mmio generation is increased even when we just start, or stop, >>> dirty logging for some memory slot, in which case users should never >>> expect all shadow pages to be zapped. >>> >>> Signed-off-by: Takuya Yoshikawa >>> --- >>> arch/x86/kvm/mmu.c | 4 +++- >>> 1 file changed, 3 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>> index c60c5da..bc8302f 100644 >>> --- a/arch/x86/kvm/mmu.c >>> +++ b/arch/x86/kvm/mmu.c >>> @@ -4385,8 +4385,10 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm) >>> * The max value is MMIO_MAX_GEN - 1 since it is not called >>> * when mark memslot invalid. >>> */ >>> - if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) >>> + if (unlikely(kvm_current_mmio_generation(kvm) >= (MMIO_MAX_GEN - 1))) { >>> + printk(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound"); >> >> This should at least be rate-limited, because it is guest triggerable. >> > It will be hard for guest to triggers it 1 << 19 times too fast though. > >> But why isn't the kvm_mmu_invalidate_zap_all_pages tracepoint enough? > > This one will trigger during slot deletion/move too. > > I would put it in to see if it actually triggers in some real world > workloads (skipping the firs wraparound since it is intentional), > we can always drop it if it will turn out to create a lot of noise. Reading a ROM in a loop can trigger it in less than 5 minutes on my machine. Not a lot of noise, but enough to be annoying. I think the existing tracepoint is enough, or we can add a more specific one here. Paolo