Re: [Qemu-devel] MSI interrupt support with vioscsi.c miniport driver

[Nicholas A. Bellinger]

On Tue, 2014-02-18 at 13:00 -0800, Nicholas A. Bellinger wrote:
> On Mon, 2014-02-10 at 11:05 -0800, Nicholas A. Bellinger wrote:
> 
> <SNIP>
> 
> > > > > Hi Yan,
> > > > > 
> > > > > So recently I've been doing some KVM guest performance comparisons
> > > > > between the scsi-mq prototype using virtio-scsi + vhost-scsi, and
> > > > > Windows Server 2012 with vioscsi.sys (virtio-win-0.1-74.iso) +
> > > > > vhost-scsi using PCIe flash backend devices.
> > > > > 
> > > > > I've noticed that small block random performance for the MSFT guest is
> > > > > at around ~80K IOPs with multiple vioscsi LUNs + adapters, which ends 
> > > > > up
> > > > > being well below what the Linux guest with scsi-mq + virtio-scsi is
> > > > > capable of (~500K).
> > > > > 
> > > > > After searching through the various vioscsi registry settings, it
> > > > > appears that MSIEnabled is being explicitly disabled (0x00000000), 
> > > > > that
> > > > > is different from what vioscsi.inx is currently defining:
> > > > > 
> > > > > [pnpsafe_pci_addreg_msix]
> > > > > HKR, "Interrupt Management",, 0x00000010
> > > > > HKR, "Interrupt Management\MessageSignaledInterruptProperties",, 
> > > > > 0x00000010
> > > > > HKR, "Interrupt Management\MessageSignaledInterruptProperties", 
> > > > > MSISupported, 0x00010001, 0
> > > > > HKR, "Interrupt Management\MessageSignaledInterruptProperties", 
> > > > > MessageNumberLimit, 0x00010001, 4
> > > > > 
> > > > > Looking deeper at vioscsi.c code, I've noticed that MSI_SUPPORTED=0 is
> > > > > explicitly disabled at build time in SOURCES + vioscsi.vcxproj, as 
> > > > > well
> > > > > as VioScsiFindAdapter() code always ends setting msix_enabled = FALSE
> > > > > here, regardless of MSI_SUPPORTED:
> > > > > 
> > > > >  
> > > > > https://github.com/YanVugenfirer/kvm-guest-drivers-windows/blob/master/vioscsi/vioscsi.c#L340
> > > > > 
> > > > > Also looking at virtio_stor.c for the raw block driver, 
> > > > > MSI_SUPPORTED=1
> > > > > appears to be the default setting for the driver included in the 
> > > > > offical
> > > > > virtio-win iso builds, right..?
> > > > > 
> > > > > Sooo, I'd like to try enabling MSI_SUPPORTED=1 in a test vioscsi.sys
> > > > > build of my own, but before going down the WDK development rabbit 
> > > > > whole,
> > > > > I'd like to better understand why you've explicitly disabled this 
> > > > > logic
> > > > > within vioscsi.c code to start..?
> > > > > 
> > > > > Is there anything that needs to be addressed / carried over from
> > > > > virtio_stor.c in order to get MSI_SUPPORTED=1 to work with vioscsi.c
> > > > > miniport code..?
> > > 
> > > Hi Nicholas,
> > > 
> > > I was thinking about enabling MSI in RHEL 6.6 (build 74) but for some
> > > reasons decided to keep it disabled until adding mq support.
> > > 
> > > 
> > > You definitely should be able to turn on MSI_SUPPORTED, rebuild the
> > > driver, and switch MSISupported to 1 to make vioscsi driver working in
> > > MSI mode.
> > >    
> > 
> > Thanks for the quick response.  We'll give MSI_SUPPORTED=1 a shot over
> > the next days with a test build on Server 2012 / Server 2008 R2 and see
> > how things go..
> > 
> 
> Just a quick update on progress.
> 
> I've been able to successfully build + load a unsigned vioscsi.sys
> driver on Server 2012 with WDK 8.0.
> 
> Running with MSI_SUPPORTED=1 against vhost-scsi results in a significant
> performance and efficiency gain, on the order of 100K to 225K IOPs for
> 4K block random I/O workload, depending on read/write mix.
> 

One other performance related question..

In vioscsi.c:VioScsiFindAdapter() code, the default setting for
adaptExt->queue_depth ends up getting set to 32 (pageNum / 4) when
indirect mode is enabled in the following bits:

    if(adaptExt->indirect) {
        adaptExt->queue_depth = max(2, (pageNum / 4));
    } else {
        adaptExt->queue_depth = pageNum / ConfigInfo->NumberOfPhysicalBreaks - 
1;
    }

Looking at viostor/virtio_stor.c:VirtIoFindAdapter() code, the default
setting for ->queue_depth appears to be 128 (pageNum):

#if (INDIRECT_SUPPORTED)
    if(!adaptExt->dump_mode) {
        adaptExt->indirect = CHECKBIT(adaptExt->features, 
VIRTIO_RING_F_INDIRECT_DESC);
    }
    if(adaptExt->indirect) {
        adaptExt->queue_depth = pageNum;
    }
#else
    adaptExt->indirect = 0;
#endif

Is there a reason for the lower queue_depth for vioscsi vs. viostor..?

How about using min(adaptExt->scsi_config.cmd_per_lun, pageNum) instead..?

Thanks!

-nab