Re: [Xen-devel] [PATCH v2 2/2] xen/pci: Use APIC directly when APIC virtualization is supported by hardware

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 10/27/2014 02:39 PM, Konrad Rzeszutek Wilk wrote:
> On Mon, Oct 27, 2014 at 12:05:53PM -0400, Boris Ostrovsky wrote:
> > When hardware supports APIC/x2APIC virtualization we don't need to use pirqs
> > for MSI handling and instead use APIC since most APIC accesses (MMIO or MSR)
> > will now be processed without VMEXITs.
> >
> > As an example, netperf on the original code produces this profile
> > (collected wih 'xentrace -e 0x0008ffff -T 5'):
> >
> >      342 cpu_change
> >      260 CPUID
> >    34638 HLT
> >    64067 INJ_VIRQ
> >    28374 INTR
> >    82733 INTR_WINDOW
> >       10 NPF
> >    24337 TRAP
> >   370610 vlapic_accept_pic_intr
> >   307528 VMENTRY
> >   307527 VMEXIT
> >   140998 VMMCALL
> >      127 wrap_buffer
> >
> > After applying this patch the same test shows
> >
> >      230 cpu_change
> >      260 CPUID
> >    36542 HLT
> >      174 INJ_VIRQ
> >    27250 INTR
> >      222 INTR_WINDOW
> >       20 NPF
> >    24999 TRAP
> >   381812 vlapic_accept_pic_intr
> >   166480 VMENTRY
> >   166479 VMEXIT
> >    77208 VMMCALL
> >       81 wrap_buffer
> >
> > ApacheBench results (ab -n 10000 -c 200) improve by about 10%
> What type of NIC did you use for this?
Intel I350 card, igb driver. I probably should have mentioned this in 
the commit message.
-boris


> Thanks!
> > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > ---
> >   arch/x86/include/asm/xen/cpuid.h |   91 ++++++++++++++++++++++++++++++++++++++
> >   arch/x86/pci/xen.c               |    9 ++++
> >   2 files changed, 100 insertions(+), 0 deletions(-)
> >   create mode 100644 arch/x86/include/asm/xen/cpuid.h
> >
> > diff --git a/arch/x86/include/asm/xen/cpuid.h b/arch/x86/include/asm/xen/cpuid.h
> > new file mode 100644
> > index 0000000..0d809e9
> > --- /dev/null
> > +++ b/arch/x86/include/asm/xen/cpuid.h
> > @@ -0,0 +1,91 @@
> > +/******************************************************************************
> > + * arch-x86/cpuid.h
> > + *
> > + * CPUID interface to Xen.
> > + *
> > + * Permission is hereby granted, free of charge, to any person obtaining a copy
> > + * of this software and associated documentation files (the "Software"), to
> > + * deal in the Software without restriction, including without limitation the
> > + * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
> > + * sell copies of the Software, and to permit persons to whom the Software is
> > + * furnished to do so, subject to the following conditions:
> > + *
> > + * The above copyright notice and this permission notice shall be included in
> > + * all copies or substantial portions of the Software.
> > + *
> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
> > + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> > + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> > + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> > + * DEALINGS IN THE SOFTWARE.
> > + *
> > + * Copyright (c) 2007 Citrix Systems, Inc.
> > + *
> > + * Authors:
> > + *    Keir Fraser <keir@xxxxxxx>
> > + */
> > +
> > +#ifndef __XEN_PUBLIC_ARCH_X86_CPUID_H__
> > +#define __XEN_PUBLIC_ARCH_X86_CPUID_H__
> > +
> > +/*
> > + * For compatibility with other hypervisor interfaces, the Xen cpuid leaves
> > + * can be found at the first otherwise unused 0x100 aligned boundary starting
> > + * from 0x40000000.
> > + *
> > + * e.g If viridian extensions are enabled for an HVM domain, the Xen cpuid
> > + * leaves will start at 0x40000100
> > + */
> > +
> > +#define XEN_CPUID_FIRST_LEAF 0x40000000
> > +#define XEN_CPUID_LEAF(i)    (XEN_CPUID_FIRST_LEAF + (i))
> > +
> > +/*
> > + * Leaf 1 (0x40000x00)
> > + * EAX: Largest Xen-information leaf. All leaves up to an including @EAX
> > + *      are supported by the Xen host.
> > + * EBX-EDX: "XenVMMXenVMM" signature, allowing positive identification
> > + *      of a Xen host.
> > + */
> > +#define XEN_CPUID_SIGNATURE_EBX 0x566e6558 /* "XenV" */
> > +#define XEN_CPUID_SIGNATURE_ECX 0x65584d4d /* "MMXe" */
> > +#define XEN_CPUID_SIGNATURE_EDX 0x4d4d566e /* "nVMM" */
> > +
> > +/*
> > + * Leaf 2 (0x40000x01)
> > + * EAX[31:16]: Xen major version.
> > + * EAX[15: 0]: Xen minor version.
> > + * EBX-EDX: Reserved (currently all zeroes).
> > + */
> > +
> > +/*
> > + * Leaf 3 (0x40000x02)
> > + * EAX: Number of hypercall transfer pages. This register is always guaranteed
> > + *      to specify one hypercall page.
> > + * EBX: Base address of Xen-specific MSRs.
> > + * ECX: Features 1. Unused bits are set to zero.
> > + * EDX: Features 2. Unused bits are set to zero.
> > + */
> > +
> > +/* Does the host support MMU_PT_UPDATE_PRESERVE_AD for this guest? */
> > +#define _XEN_CPUID_FEAT1_MMU_PT_UPDATE_PRESERVE_AD 0
> > +#define XEN_CPUID_FEAT1_MMU_PT_UPDATE_PRESERVE_AD  (1u<<0)
> > +
> > +/*
> > + * Leaf 5 (0x40000x04)
> > + * HVM-specific features
> > + */
> > +
> > +/* EAX Features */
> > +/* Virtualized APIC registers */
> > +#define XEN_HVM_CPUID_APIC_ACCESS_VIRT (1u << 0)
> > +/* Virtualized x2APIC accesses */
> > +#define XEN_HVM_CPUID_X2APIC_VIRT      (1u << 1)
> > +/* Memory mapped from other domains has valid IOMMU entries */
> > +#define XEN_HVM_CPUID_IOMMU_MAPPINGS   (1u << 2)
> > +
> > +#define XEN_CPUID_MAX_NUM_LEAVES 4
> > +
> > +#endif /* __XEN_PUBLIC_ARCH_X86_CPUID_H__ */
> > diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
> > index 1370716..d768371 100644
> > --- a/arch/x86/pci/xen.c
> > +++ b/arch/x86/pci/xen.c
> > @@ -23,6 +23,7 @@
> >   #include <xen/features.h>
> >   #include <xen/events.h>
> >   #include <asm/xen/pci.h>
> > +#include <asm/xen/cpuid.h>
> >   #include <asm/i8259.h>
> >   
> >   static int xen_pcifront_enable_irq(struct pci_dev *dev)
> > @@ -434,6 +435,14 @@ int __init pci_xen_init(void)
> >   #ifdef CONFIG_PCI_MSI
> >   void __init xen_msi_init(void)
> >   {
> > +       if (!disable_apic) {
> > +               uint32_t eax = cpuid_eax(xen_cpuid_base() + 4);
> > +
> > +               if (((eax & XEN_HVM_CPUID_X2APIC_VIRT) && x2apic_mode) ||
> > +                   ((eax & XEN_HVM_CPUID_APIC_ACCESS_VIRT) && cpu_has_apic))
> > +                       return;
> > +       }
> > +
> >         x86_msi.setup_msi_irqs = xen_hvm_setup_msi_irqs;
> >         x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
> >   }
> > --
> > 1.7.1

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