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

[Yan Vugenfirer]

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..?
> 
> TIA!
> 
> --nab
> 
>