[lustre-discuss] LNET routes

[Chris Horn]

The route selection algorithm looks at:

1. Priority
2. Hop count
3. Number of bytes in transit (or queued)
4. Number of credits available
5. Which was used last

So, everything else being equal, step 5 will ensure round-robin. But there are several other factors that are considered first.

At least, this was true before multi-rail. I’m not sure if that has changed things w.r.t. route selection.

Chris Horn

From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of Preeti Malakar <malakar.preeti at gmail.com>
Date: Friday, January 26, 2018 at 10:28 AM
To: "lustre-discuss at lists.lustre.org" <lustre-discuss at lists.lustre.org>
Subject: [lustre-discuss] LNET routes

Hi,

I was wondering if someone can help me with the following question about LNETs:

When three writes are issued from a compute node to an OST, is it right that the order in which the LNETs (corresponding to that OST) are used to route the data from the compute node to the OST is the sequence in which LNETs are assigned to the OST, i.e. in round robin order? For e.g. if the LNETs for an OST were 14,410,1022,1246,2341,2438,3441,3594, then for three writes from a compute node, the LNETs used will be 14,410,1022. If there are writes from other nodes to the same OST at the same time, then this order (of LNETs) depends on the writes issued from other nodes as well, is that right?

Thanks,
Preeti

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