From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v12 09/11] pvqspinlock, x86: Add para-virtualization support Date: Fri, 24 Oct 2014 10:54:37 +0200 Message-ID: <20141024085437.GV21513@worktop.programming.kicks-ass.net> References: <1413483040-58399-1-git-send-email-Waiman.Long@hp.com> <1413483040-58399-10-git-send-email-Waiman.Long@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1413483040-58399-10-git-send-email-Waiman.Long@hp.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 Cc: linux-arch@vger.kernel.org, Rik van Riel , Raghavendra K T , Oleg Nesterov , kvm@vger.kernel.org, Konrad Rzeszutek Wilk , Scott J Norton , x86@kernel.org, Paolo Bonzini , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Ingo Molnar , David Vrabel , "H. Peter Anvin" , xen-devel@lists.xenproject.org, Thomas Gleixner , "Paul E. McKenney" , Linus Torvalds , Boris Ostrovsky , Douglas Hatch List-Id: linux-arch.vger.kernel.org On Thu, Oct 16, 2014 at 02:10:38PM -0400, Waiman Long wrote: > Since enabling paravirt spinlock will disable unlock function inlining, > a jump label can be added to the unlock function without adding patch > sites all over the kernel. But you don't have to. My patches allowed for the inline to remain, again reducing the overhead of enabling PV spinlocks while running on a real machine. Look at: http://lkml.kernel.org/r/20140615130154.213923590@chello.nl In particular this hunk: Index: linux-2.6/arch/x86/kernel/paravirt_patch_64.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/paravirt_patch_64.c +++ linux-2.6/arch/x86/kernel/paravirt_patch_64.c @@ -22,6 +22,10 @@ DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs") DEF_NATIVE(, mov32, "mov %edi, %eax"); DEF_NATIVE(, mov64, "mov %rdi, %rax"); +#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCK) +DEF_NATIVE(pv_lock_ops, queue_unlock, "movb $0, (%rdi)"); +#endif + unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len) { return paravirt_patch_insns(insnbuf, len, @@ -61,6 +65,9 @@ unsigned native_patch(u8 type, u16 clobb PATCH_SITE(pv_cpu_ops, clts); PATCH_SITE(pv_mmu_ops, flush_tlb_single); PATCH_SITE(pv_cpu_ops, wbinvd); +#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCK) + PATCH_SITE(pv_lock_ops, queue_unlock); +#endif patch_site: ret = paravirt_patch_insns(ibuf, len, start, end); That makes sure to overwrite the callee-saved call to the pv_lock_ops::queue_unlock with the immediate asm "movb $0, (%rdi)". Therefore you can retain the inlined unlock with hardly (there might be some NOP padding) any overhead at all. On PV it reverts to a callee saved function call. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.9]:33966 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750909AbaJXIys (ORCPT ); Fri, 24 Oct 2014 04:54:48 -0400 Date: Fri, 24 Oct 2014 10:54:37 +0200 From: Peter Zijlstra Subject: Re: [PATCH v12 09/11] pvqspinlock, x86: Add para-virtualization support Message-ID: <20141024085437.GV21513@worktop.programming.kicks-ass.net> References: <1413483040-58399-1-git-send-email-Waiman.Long@hp.com> <1413483040-58399-10-git-send-email-Waiman.Long@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1413483040-58399-10-git-send-email-Waiman.Long@hp.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Waiman Long Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Paolo Bonzini , Konrad Rzeszutek Wilk , Boris Ostrovsky , "Paul E. McKenney" , Rik van Riel , Linus Torvalds , Raghavendra K T , David Vrabel , Oleg Nesterov , Scott J Norton , Douglas Hatch Message-ID: <20141024085437.B90LQ_jL0fb_ujnv1qDYgbUWq0TQ8Fp34x8y3jYe_Fg@z> On Thu, Oct 16, 2014 at 02:10:38PM -0400, Waiman Long wrote: > Since enabling paravirt spinlock will disable unlock function inlining, > a jump label can be added to the unlock function without adding patch > sites all over the kernel. But you don't have to. My patches allowed for the inline to remain, again reducing the overhead of enabling PV spinlocks while running on a real machine. Look at: http://lkml.kernel.org/r/20140615130154.213923590@chello.nl In particular this hunk: Index: linux-2.6/arch/x86/kernel/paravirt_patch_64.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/paravirt_patch_64.c +++ linux-2.6/arch/x86/kernel/paravirt_patch_64.c @@ -22,6 +22,10 @@ DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs") DEF_NATIVE(, mov32, "mov %edi, %eax"); DEF_NATIVE(, mov64, "mov %rdi, %rax"); +#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCK) +DEF_NATIVE(pv_lock_ops, queue_unlock, "movb $0, (%rdi)"); +#endif + unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len) { return paravirt_patch_insns(insnbuf, len, @@ -61,6 +65,9 @@ unsigned native_patch(u8 type, u16 clobb PATCH_SITE(pv_cpu_ops, clts); PATCH_SITE(pv_mmu_ops, flush_tlb_single); PATCH_SITE(pv_cpu_ops, wbinvd); +#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCK) + PATCH_SITE(pv_lock_ops, queue_unlock); +#endif patch_site: ret = paravirt_patch_insns(ibuf, len, start, end); That makes sure to overwrite the callee-saved call to the pv_lock_ops::queue_unlock with the immediate asm "movb $0, (%rdi)". Therefore you can retain the inlined unlock with hardly (there might be some NOP padding) any overhead at all. On PV it reverts to a callee saved function call.