[ofw] winverbs ND provider

[Tzachi Dar]

Hi Fab,

Please see bellow.

Thanks
Tzachi

> -----Original Message-----
> From: Fab Tillier [mailto:ftillier at microsoft.com] 
> Sent: Wednesday, January 13, 2010 8:05 PM
> To: Tzachi Dar; Sean Hefty; ofw_list
> Subject: RE: [ofw] winverbs ND provider
> 
> Hi Tzachi
> 
> Tzachi Dar wrote on Wed, 13 Jan 2010 at 09:48:51
> > Just making sure, we are talking about 2008 64 bits right?
> > 
> > 
> > As for  QueryPerformanceCounter():
> > 
> > I have run a simple test routine and I get 1.2 us which is 
> outrageous 
> > in itself but still very far from your numbers.
> 
> This is fixed in Server 2008 R2.
> 
It is good to know. I must say that my measurments (on an old computer)
didn't show that.


> > As for the ibat resolve:
> > 
> > I have created a very simple "resolve" program and started playing 
> > with it. Without any change resolve takes ~33us
> > 
> > I have changed the resolve code to open the ibat device 
> once and than 
> > only do the resolve many times this took ~27us. I guess that the nd 
> > code can do a similar thing.
> 
> When does the file get closed?  How do you get the 
> application to close the file if, say, IPoIB gets disabled?  
> Say you have a service that keeps track of IP address 
> arrival/removal, so that it's not necessarily doing anything 
> over IB when IPoIB is disabled.  How do you trigger the 
> service to close the IBAT device?
> 
> So while you might be able to save 5us by avoiding opening 
> the file, you introduce issues that aren't worth the 
> benefits.  I'm sure you'd be able to shave off 5us, if not 
> more, by making the QP modify asynchronous.
> 

The only problem of the file not being closed is the fact that the ipoib
driver can not go down (the ports themselves can be disabled).
The same approach is being used by WSD which opens the ibat device once
going up and only closes it while going down.
Since WSD usually loads into services that never go down this means that
ipoib can not go down as well. Not that nice when developing the system
but probably good enough for a user.
There is also a solution to this problem by having some notification
mechanism that will ask ibal to close the device when all prots are
down.

That said, I agree that when looking at the big picture this 5us are not
that important. It currently takes us around 800us to complete a
connection and I'm still not sure where is that time being waisted.





> -Fab
>