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

[Nicholas A. Bellinger]

Hi Vadim & Yan,

On Sun, 2014-02-09 at 22:35 +1100, Vadim Rozenfeld wrote:
> On Sun, 2014-02-09 at 11:24 +0200, Yan Vugenfirer wrote:
> > Hi Nicholas,
> > 
> > Adding Vadim Rozenfeld who wrote the virtio-scsi driver.
> > 
> > Best regards,
> > Yan.
> > 
> > On Feb 7, 2014, at 10:14 PM, Nicholas A. Bellinger <address@hidden> wrote:
> > 
> > > 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..

Thanks again!

--nab