From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933785AbdKGMYT (ORCPT ); Tue, 7 Nov 2017 07:24:19 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54788 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752027AbdKGMYR (ORCPT ); Tue, 7 Nov 2017 07:24:17 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 555605D9E5 Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=pbonzini@redhat.com Subject: Re: [PATCHv3 1/1] locking/qspinlock/x86: Avoid test-and-set when PV_DEDICATED is set To: Eduardo Valentin , rkrcmar@redhat.com Cc: Matt Wilson , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Peter Zijlstra , Waiman Long , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, "Jan H . Schoenherr" , Anthony Liguori References: <1509999980-10828-1-git-send-email-eduval@amazon.com> From: Paolo Bonzini Message-ID: <593c8cc3-f532-1868-c80f-7ef2511c7e15@redhat.com> Date: Tue, 7 Nov 2017 13:23:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1509999980-10828-1-git-send-email-eduval@amazon.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Tue, 07 Nov 2017 12:24:17 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/11/2017 21:26, Eduardo Valentin wrote: > Currently, the existing qspinlock implementation will fallback to > test-and-set if the hypervisor has not set the PV_UNHALT flag. > > This patch gives the opportunity to guest kernels to select > between test-and-set and the regular queueu fair lock implementation > based on the PV_DEDICATED KVM feature flag. When the PV_DEDICATED > flag is not set, the code will still fall back to test-and-set, > but when the PV_DEDICATED flag is set, the code will use > the regular queue spinlock implementation. > > With this patch, when in autoselect mode, the guest will > use the default spinlock implementation based on host feature > flags as follows: > > PV_DEDICATED = 1, PV_UNHALT = anything: default is qspinlock > PV_DEDICATED = 0, PV_UNHALT = 1: default is pvqspinlock > PV_DEDICATED = 0, PV_UNHALT = 0: default is tas Hi Eduardo, besides the suggestion to use a separate word than the one for features, is this still needed after Waiman's patch to adaptively switch between tas and pvqspinlock? Paolo > Cc: Paolo Bonzini > Cc: "Radim Krčmář" > Cc: Jonathan Corbet > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: "H. Peter Anvin" > Cc: x86@kernel.org > Cc: Peter Zijlstra > Cc: Waiman Long > Cc: kvm@vger.kernel.org > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: Jan H. Schoenherr > Cc: Anthony Liguori > Suggested-by: Matt Wilson > Signed-off-by: Eduardo Valentin > --- > V3: > - When PV_DEDICATED is set (1), qspinlock is selected, > regardless of the value of PV_UNHAULT. Suggested by Paolo Bonzini. > - Refreshed on top of tip/master. > V2: > - rebase on top of tip/master > > Documentation/virtual/kvm/cpuid.txt | 6 ++++++ > arch/x86/include/asm/qspinlock.h | 4 ++++ > arch/x86/include/uapi/asm/kvm_para.h | 1 + > arch/x86/kernel/kvm.c | 2 ++ > 4 files changed, 13 insertions(+) > > diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt > index 3c65feb..117066a 100644 > --- a/Documentation/virtual/kvm/cpuid.txt > +++ b/Documentation/virtual/kvm/cpuid.txt > @@ -54,6 +54,12 @@ KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit > || || before enabling paravirtualized > || || spinlock support. > ------------------------------------------------------------------------------ > +KVM_FEATURE_PV_DEDICATED || 8 || guest checks this feature bit > + || || to determine if they run on > + || || dedicated vCPUs, allowing opti- > + || || mizations such as usage of > + || || qspinlocks. > +------------------------------------------------------------------------------ > KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side > || || per-cpu warps are expected in > || || kvmclock. > diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h > index 5e16b5d..de42694 100644 > --- a/arch/x86/include/asm/qspinlock.h > +++ b/arch/x86/include/asm/qspinlock.h > @@ -3,6 +3,8 @@ > #define _ASM_X86_QSPINLOCK_H > > #include > +#include > + > #include > #include > #include > @@ -58,6 +60,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock) > if (!static_branch_likely(&virt_spin_lock_key)) > return false; > > + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) > + return false; > /* > * On hypervisors without PARAVIRT_SPINLOCKS support we fall > * back to a Test-and-Set spinlock, because fair locks have > diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h > index 554aa8f..85a9875 100644 > --- a/arch/x86/include/uapi/asm/kvm_para.h > +++ b/arch/x86/include/uapi/asm/kvm_para.h > @@ -25,6 +25,7 @@ > #define KVM_FEATURE_STEAL_TIME 5 > #define KVM_FEATURE_PV_EOI 6 > #define KVM_FEATURE_PV_UNHALT 7 > +#define KVM_FEATURE_PV_DEDICATED 8 > > /* The last 8 bits are used to indicate how to interpret the flags field > * in pvclock structure. If no bits are set, all flags are ignored. > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 8bb9594..dacd7cf 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -642,6 +642,8 @@ void __init kvm_spinlock_init(void) > { > if (!kvm_para_available()) > return; > + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) > + return; > /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ > if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) > return; >