RE: [Xen-devel] RE: Rather slow time of Pin in Windows with GPL PVdriver

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

NDIS 5.x on Vista+ has some serious issues: see 
http://www.osronline.com/showThread.cfm?link=124242

This probably doesn't explain an immediate performance issue though. RSS is 
supported on Windows 2k3 SP2 IIRC but you need to bind as NDIS 5.2. I don't 
think it's present in the 6.x -> 5.x wrapper in Vista+ though. You'd need to 
use NDIS 6.1+.

  Paul

> -----Original Message-----
> From: James Harper [mailto:james.harper@xxxxxxxxxxxxxxxx]
> Sent: 14 March 2011 00:46
> To: MaoXiaoyun; Paul Durrant
> Cc: xen devel
> Subject: RE: [Xen-devel] RE: Rather slow time of Pin in Windows with
> GPL PVdriver
> 
> >
> > I've just pushed a bit of a rewrite of the rx path in gplpv. It's
> not
> > particularly well tested yet but I can't get it to crash. It
> should
> scale much
> > better with SMP too. I'm using more lock free data structures so
> the
> lock's
> > are held for much less time.
> >
> 
> Unfortunately performance still isn't good. What I've found is that
> NDIS really does want you to only process packets on one CPU at one
> time (eg CPU0), otherwise they are indicated to NDIS out of order
> causing serious performance problems (according to the docs).
> 
> In addition to KeSetTargetProcessorDpc(&xi->rx_dpc, 0), we also need
> to do KeSetImportanceDpc(&xi->rx_dpc, HighImportance) - as Paul
> stated, which makes sure the DPC runs immediately even if it is
> triggered from another CPU (I assume this has IPI overhead though).
> I think I could detect >1 CPU's and schedule the rx and tx onto
> different CPU's to each other, but always the same CPU.
> 
> Windows does support RSS which ensures per-connection in-order
> processing of packets. From reading the "Receive-Side Scaling
> Enhancements in Windows Server 2008" document, it appears that we
> would need to hash various fields in the packet header and compute a
> CPU number for that connection, then schedule the DPC onto that CPU.
> It shouldn't be that hard except that xennet.sys is an NDIS5.1
> driver, not an NDIS6.0 driver, and in order to support NDIS6.0 I
> would need to maintain two trees which I'm reluctant to do without a
> very good reason.
> Other docs state the RSS is supported for Windows 2003 SP2 but I
> can't find any specifics - I've asked the question on the ntdev
> list.
> 
> James

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