From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [PATCH 0/6] x86: reduce paravirtualized spinlock overhead Date: Mon, 04 May 2015 07:55:07 +0200 Message-ID: <554709BB.7090400@suse.com> References: <1430391243-7112-1-git-send-email-jgross@suse.com> <55425ADA.4060105@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55425ADA.4060105@goop.org> 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: Jeremy Fitzhardinge , linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com, xen-devel@lists.xensource.com, konrad.wilk@oracle.com, david.vrabel@citrix.com, boris.ostrovsky@oracle.com, chrisw@sous-sol.org, akataria@vmware.com, rusty@rustcorp.com.au, virtualization@lists.linux-foundation.org, gleb@kernel.org, pbonzini@redhat.com, kvm@vger.kernel.org List-Id: virtualization@lists.linuxfoundation.org On 04/30/2015 06:39 PM, Jeremy Fitzhardinge wrote: > On 04/30/2015 03:53 AM, Juergen Gross wrote: >> Paravirtualized spinlocks produce some overhead even if the kernel is >> running on bare metal. The main reason are the more complex locking >> and unlocking functions. Especially unlocking is no longer just one >> instruction but so complex that it is no longer inlined. >> >> This patch series addresses this issue by adding two more pvops >> functions to reduce the size of the inlined spinlock functions. When >> running on bare metal unlocking is again basically one instruction. > > Out of curiosity, is there a measurable difference? I did a small measurement of the pure locking functions on bare metal without and with my patches. spin_lock() for the first time (lock and code not in cache) dropped from about 600 to 500 cycles. spin_unlock() for first time dropped from 145 to 87 cycles. spin_lock() in a loop dropped from 48 to 45 cycles. spin_unlock() in the same loop dropped from 24 to 22 cycles. Juergen