Re: Performance test result between virtio_pci MSI-X disable and enable

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Dec 01, 2010 at 04:41:38PM +0800, lidong chen wrote:
> I used sr-iov, give each vm 2 vf.
> after apply the patch, and i found performence is the same.
> 
> the reason is in function msix_mmio_write, mostly addr is not in mmio range.
> 
> static int msix_mmio_write(struct kvm_io_device *this, gpa_t addr, int len,
> 			   const void *val)
> {
> 	struct kvm_assigned_dev_kernel *adev =
> 			container_of(this, struct kvm_assigned_dev_kernel,
> 				     msix_mmio_dev);
> 	int idx, r = 0;
> 	unsigned long new_val = *(unsigned long *)val;
> 
> 	mutex_lock(&adev->kvm->lock);
> 	if (!msix_mmio_in_range(adev, addr, len)) {
> 		// return here.
>                  r = -EOPNOTSUPP;
> 		goto out;
> 	}
> 
> i printk the value:
> addr             start           end           len
> F004C00C   F0044000  F0044030     4
> 
> 00:06.0 Ethernet controller: Intel Corporation Unknown device 10ed (rev 01)
> 	Subsystem: Intel Corporation Unknown device 000c
> 	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
> Stepping- SERR- FastB2B-
> 	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort-
> <TAbort- <MAbort- >SERR- <PERR-
> 	Latency: 0
> 	Region 0: Memory at f0040000 (32-bit, non-prefetchable) [size=16K]
> 	Region 3: Memory at f0044000 (32-bit, non-prefetchable) [size=16K]
> 	Capabilities: [40] MSI-X: Enable+ Mask- TabSize=3
> 		Vector table: BAR=3 offset=00000000
> 		PBA: BAR=3 offset=00002000
> 
> 00:07.0 Ethernet controller: Intel Corporation Unknown device 10ed (rev 01)
> 	Subsystem: Intel Corporation Unknown device 000c
> 	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
> Stepping- SERR- FastB2B-
> 	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort-
> <TAbort- <MAbort- >SERR- <PERR-
> 	Latency: 0
> 	Region 0: Memory at f0048000 (32-bit, non-prefetchable) [size=16K]
> 	Region 3: Memory at f004c000 (32-bit, non-prefetchable) [size=16K]
> 	Capabilities: [40] MSI-X: Enable+ Mask- TabSize=3
> 		Vector table: BAR=3 offset=00000000
> 		PBA: BAR=3 offset=00002000
> 
> 
> 
> +static bool msix_mmio_in_range(struct kvm_assigned_dev_kernel *adev,
> +			      gpa_t addr, int len)
> +{
> +	gpa_t start, end;
> +
> +	BUG_ON(adev->msix_mmio_base == 0);
> +	start = adev->msix_mmio_base;
> +	end = adev->msix_mmio_base + PCI_MSIX_ENTRY_SIZE *
> +		adev->msix_max_entries_nr;
> +	if (addr >= start && addr + len <= end)
> +		return true;
> +
> +	return false;
> +}


Hmm, this check looks wrong to me: there's no guarantee
that guest uses the first N entries in the table.
E.g. it could use a single entry, but only the last one.

> 
> 
> 2010/11/30 Yang, Sheng <sheng.yang@intel.com>:
> > On Tuesday 30 November 2010 17:10:11 lidong chen wrote:
> >> sr-iov also meet this problem, MSIX mask waste a lot of cpu resource.
> >>
> >> I test kvm with sriov, which the vf driver could not disable msix.
> >> so the host os waste a lot of cpu.  cpu rate of host os is 90%.
> >>
> >> then I test xen with sriov, there ara also a lot of vm exits caused by
> >> MSIX mask.
> >> but the cpu rate of xen and domain0 is less than kvm. cpu rate of xen
> >> and domain0 is 60%.
> >>
> >> without sr-iov, the cpu rate of xen and domain0 is higher than kvm.
> >>
> >> so i think the problem is kvm waste more cpu resource to deal with MSIX
> >> mask. and we can see how xen deal with MSIX mask.
> >>
> >> if this problem sloved, maybe with MSIX enabled, the performace is better.
> >
> > Please refer to my posted patches for this issue.
> >
> > http://www.spinics.net/lists/kvm/msg44992.html
> >
> > --
> > regards
> > Yang, Sheng
> >
> >>
> >> 2010/11/23 Avi Kivity <avi@redhat.com>:
> >> > On 11/23/2010 09:27 AM, lidong chen wrote:
> >> >> can you tell me something about this problem.
> >> >> thanks.
> >> >
> >> > Which problem?
> >> >
> >> > --
> >> > I have a truly marvellous patch that fixes the bug which this
> >> > signature is too narrow to contain.
> >