[ofa-general] [PATCH] opensm: Parallelize (Stripe) LFT sets across switches

[Jason Gunthorpe]

On Thu, Jul 23, 2009 at 03:53:07PM +0300, Yevgeny Kliteynik wrote:
> >I would be very surprised if any implementation had a significant
> >overhead for the actual set operation compared to the packet handling
> >path. Certainly in our products the incremental cost of a set vs
> >processing a DR is negligible. I expect similar results from any
> >switch. As soon as a SMP goes into the CPU for DR or other processing
> >there is an enormous hit.
> 
> Whether the DR packets forwarding is done in HW, FW or SW is
> implementation dependent. I agree with you that if the same
> entity is processing LFT block set and DR MAD forwarding, then
> the difference between these two operations would not be very
> big (having said that, I'm not sure it's negligible - again,
> it's implementation dependent).
> 
> I don't know about all the IB switches, but in InfiniScale IV
> (and any InfiniScaleIV-based switches out there) DR packets
> forwarding is done in HW, so its significantly faster than
> processing LFT block by the SMA.

Yes, this is sort of what worries me.. Tuning/testing for these kind
of switches can horribly break on other switches that have low limits
on DR SMP processing.

Jason