From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Ostrovsky Subject: Re: [PATCH] x86/paravirt: Add kernel parameter to choose paravirt lock type Date: Wed, 1 Nov 2017 15:01:21 -0400 Message-ID: <5539b95d-eac4-cc09-2cfc-1452d2751fa0@oracle.com> References: <1509550367-19255-1-git-send-email-longman@redhat.com> <404a9fab-03ff-174e-4ece-79932a6f302c@suse.com> <409ede92-5243-0d9b-7893-b596f3f353aa@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <409ede92-5243-0d9b-7893-b596f3f353aa@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Waiman Long , Juergen Gross , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Jonathan Corbet Cc: Rusty Russell , kvm@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Peter Zijlstra , x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Paolo Bonzini , xen-devel@lists.xenproject.org, Alok Kataria List-Id: virtualization@lists.linuxfoundation.org On 11/01/2017 12:28 PM, Waiman Long wrote: > On 11/01/2017 11:51 AM, Juergen Gross wrote: >> On 01/11/17 16:32, Waiman Long wrote: >>> Currently, there are 3 different lock types that can be chosen for >>> the x86 architecture: >>> >>> - qspinlock >>> - pvqspinlock >>> - unfair lock >>> >>> One of the above lock types will be chosen at boot time depending on >>> a number of different factors. >>> >>> Ideally, the hypervisors should be able to pick the best performing >>> lock type for the current VM configuration. That is not currently >>> the case as the performance of each lock type are affected by many >>> different factors like the number of vCPUs in the VM, the amount vCPU >>> overcommitment, the CPU type and so on. >>> >>> Generally speaking, unfair lock performs well for VMs with a small >>> number of vCPUs. Native qspinlock may perform better than pvqspinlock >>> if there is vCPU pinning and there is no vCPU over-commitment. >>> >>> This patch adds a new kernel parameter to allow administrator to >>> choose the paravirt spinlock type to be used. VM administrators can >>> experiment with the different lock types and choose one that can best >>> suit their need, if they want to. Hypervisor developers can also use >>> that to experiment with different lock types so that they can come >>> up with a better algorithm to pick the best lock type. >>> >>> The hypervisor paravirt spinlock code will override this new parameter >>> in determining if pvqspinlock should be used. The parameter, however, >>> will override Xen's xen_nopvspin in term of disabling unfair lock. >> Hmm, I'm not sure we need pvlock_type _and_ xen_nopvspin. What do others >> think? > I don't think we need xen_nopvspin, but I don't want to remove that > without agreement from the community. I also don't think xen_nopvspin will be needed after pvlock_type is introduced. -boris