Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757194AbaJ2UZU (ORCPT ); Wed, 29 Oct 2014 16:25:20 -0400 Received: from g4t3427.houston.hp.com ([15.201.208.55]:53449 "EHLO g4t3427.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755321AbaJ2UZP (ORCPT ); Wed, 29 Oct 2014 16:25:15 -0400 Message-ID: <54514D25.4020207@hp.com> Date: Wed, 29 Oct 2014 16:25:09 -0400 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Peter Zijlstra 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 Subject: Re: [PATCH v12 09/11] pvqspinlock, x86: Add para-virtualization support 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> <544E830C.6070307@hp.com> <20141027180439.GL3337@twins.programming.kicks-ass.net> <544EB79E.6020200@hp.com> <54513A90.3080108@hp.com> In-Reply-To: <54513A90.3080108@hp.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/29/2014 03:05 PM, Waiman Long wrote: > On 10/27/2014 05:22 PM, Waiman Long wrote: >> On 10/27/2014 02:04 PM, Peter Zijlstra wrote: >>> On Mon, Oct 27, 2014 at 01:38:20PM -0400, Waiman Long wrote: >>>> 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? >>> modules should be fine, see arch/x86/kernel/module.c:module_finalize() >>> -> apply_paravirt(). >>> >>> Also note that the 'default' text is an indirect call into the paravirt >>> ops table which routes to the 'right' function, so even if the text >>> patching would be 'late' calls would 'work' as expected, just slower. >> >> Thanks for letting me know about that. I have this concern because >> your patch didn't change the current configuration of disabling >> unlock inlining when paravirt_spinlock is enabled. With that, I think >> it is worthwhile to reduce the performance delta between the PV and >> non-PV kernel on bare metal. > > I am sorry that the unlock call sites patching code doesn't work in a > virtual guest. Your pvqspinlock patch did an unconditional patching > even in a virtual guest. I added check for the > paravirt_spinlocks_enabled, but it turned out that some spin_unlock() > seemed to be called before paravirt_spinlocks_enabled is set. As a > result, some call sites were still patched resulting in missed wake > up's and system hang. > > At this point, I am going to leave out that change from my patch set > until we can figure out a better way of doing that. > Below was a partial kernel log with the unlock call site patch code in a KVM guest: [ 0.438006] native_patch: patch out pv_queue_unlock! [ 0.438565] native_patch: patch out pv_queue_unlock! [ 0.439006] native_patch: patch out pv_queue_unlock! [ 0.439638] native_patch: patch out pv_queue_unlock! [ 0.440052] native_patch: patch out pv_queue_unlock! [ 0.441006] native_patch: patch out pv_queue_unlock! [ 0.441566] native_patch: patch out pv_queue_unlock! [ 0.442035] ftrace: allocating 24168 entries in 95 pages [ 0.451208] Switched APIC routing to physical flat. [ 0.453202] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1 [ 0.454002] smpboot: CPU0: Intel QEMU Virtual CPU version 1.5.3 (fam: 06, model: 06, stepping: 03) [ 0.456000] Performance Events: Broken PMU hardware detected, using software events only. [ 0.456003] Failed to access perfctr msr (MSR c1 is 0) [ 0.457151] KVM setup paravirtual spinlock [ 0.460039] NMI watchdog: disabled (cpu0): hardware events not enabled It could be seen that some unlock call sites were patched before the KVM setup code set the paravirt_spinlocks_enabled flag. -Longman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/