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

[Wangting (Kathy)]

> On Tue, 2014-02-18 at 13:11 -0800, Nicholas A. Bellinger wrote:
>> 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..?
> 
> It's a horrible work around for the following bug:
> https://bugzilla.redhat.com/show_bug.cgi?id=1013443
> 
> I'm going to remove it as soon as found better solution for it.
> 
> Best regards,
> Vadim.
> 
> 
Hi Vadim,

I have found that Bug 1013443 has been closed with a
resolution of ERRATA.

The windows device queue must be between 20 and 254
for StorPortSetDeviceQueueDepth to succeed.

So I have the question that why queue_depth can not be
set to pageNum(128)?

Best wishes,
Ting Wang

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