From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v12 09/11] pvqspinlock, x86: Add para-virtualization support Date: Mon, 27 Oct 2014 13:38:20 -0400 Message-ID: <544E830C.6070307__38673.0126374916$1414431608$gmane$org@hp.com> References: <1413483040-58399-1-git-send-email-Waiman.Long@hp.com> <1413483040-58399-10-git-send-email-Waiman.Long@hp.com> <20141024085437.GV21513@worktop.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1XioFS-0002ga-Qj for xen-devel@lists.xenproject.org; Mon, 27 Oct 2014 17:38:30 +0000 In-Reply-To: <20141024085437.GV21513@worktop.programming.kicks-ass.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Peter Zijlstra Cc: linux-arch@vger.kernel.org, Raghavendra K T , Oleg Nesterov , kvm@vger.kernel.org, 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: xen-devel@lists.xenproject.org On 10/24/2014 04:54 AM, Peter Zijlstra wrote: > 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. My concern is that spin_unlock() can be called in many places, including loadable kernel modules. Can the paravirt_patch_ident_32() function able to patch all of them in reasonable time? How about a kernel module loaded later at run time? So I think we may still need to disable unlock function inlining even if we used your way kernel site patching. Regards, Longman