Jim Schutt wrote:
Or Gerlitz wrote:
Roland Dreier wrote:
Bob Pearson <[email protected]> wrote:
With lash+mesh redsky required 6-7 VLs to wire up without deadlocks.
I think
that Jim's version uses 8 SLs but only 2VLs to work.
If someone was using a torus and also wanted to support QOS and also
wanted
to separate multicast and management on a separate VL to be
absolutely sure
that there is no possibility of a deadlock you might end up with
#QOS * 2 +
1 which would be 5 using the current algorithm.
But again you don't need all those VLs on the HCAs' links, do you?
Jason Gunthorpe wrote:
Routing algorithms only need VLs on interswitch links, not on HCA to
switch links. The only use of the HCA to switch VLs is for QoS. Mesh
topologies can usually be routed with only two VLs, but you need alot
of SLs to make that work.
Bob, Jim, Alex
I wasn't sure if the SL-to-VL mapping done by open SM is dictated by
the directives @ the user config file or if the routing algorithm is
"VL aware" but the routing engine? if the latter, do interswitch links
use different mapping vs. HCA - switch links?
FWIW, the torus-2QoS routing engine uses VL bit 0 for torus deadlock
avoidance, VL bit 1 to route around a missing switch without deadlocks,
and VL bit 2 to provide two QoS levels. It needs the port dependence
of the SL2VL maps to do this in switches.
The interswitch and HCAs use the same mapping, but only VL bit 2
is needed on HCAs, to provide the QoS levels.
It occurred to me as soon I sent the above that there's no
good reason to insist that the VL usage is the same for both
interswitch links, and switch-CA links.
Do I need to change this?
-- Jim
I chose that bit usage because it seemed the proper ordering of
capabilities if there are fewer than 8 data VLs available - basic
deadlock avoidance is most important; some QoS is nice to have but
not that useful if the fabric can deadlock.
Is that what you were asking, at least WRT. torus-2QoS?
-- Jim
Or.
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