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

[Vadim Rozenfeld <vrozenfe@redhat.com>]

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 <nab@linux-iscsi.org> 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.
   
Cheers,
Vadim.

> > 
> > TIA!
> > 
> > --nab
> > 
> > 
>