Bug 2188084

Summary: openvswitch userspace needs to provide information about selection hash availability
Product: Red Hat Enterprise Linux Fast Datapath Reporter: Aaron Conole <aconole>
Component: openvswitch3.1Assignee: Mike Pattrick <mpattric>
Status: CLOSED CURRENTRELEASE QA Contact: ovs-qe
Severity: high Docs Contact:
Priority: unspecified    
Version: FDP 23.ACC: ctrautma, dceara, fleitner, jhsiao, ralongi
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Hardware: All   
OS: Linux   
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Last Closed: 2023-07-11 13:03:09 UTC Type: Bug
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Bug Blocks: 2175716, 2188679    

Description Aaron Conole 2023-04-19 17:15:05 UTC
Description of problem:

Userspace side of the work to provide a stable l3/l4 hash.

Comment 1 Dumitru Ceara 2023-04-21 15:33:14 UTC
In theory ovs-vswitchd should already be reporting what kind of hash the datapath supports through the "Datapath.capabilities:max_hash_alg" key:
https://github.com/openvswitch/ovs/blob/d70688a7291edb432fd66b9230a92842fcfd3607/vswitchd/vswitch.xml#L6310

In practice this will always return 0 (OVS_HASH_ALG_L4) for the kernel datapath:
https://github.com/openvswitch/ovs/blob/d70688a7291edb432fd66b9230a92842fcfd3607/ofproto/ofproto-dpif.c#L1439

/* Data path hash algorithm for computing Datapath hash.
 *
 * The algorithm type only specifies the fields in a flow
 * will be used as part of the hash. Each datapath is free
 * to use its own hash algorithm. The hash value will be
 * opaque to the user space daemon.
 */
enum ovs_hash_alg {
	OVS_HASH_ALG_L4,
#ifndef __KERNEL__
	OVS_HASH_ALG_SYM_L4,
#endif
	__OVS_HASH_MAX
};

I'm not sure if the stable hash we need for the kernel datapath will end up being a symmetric one but if it does we could try to just use the Datapath.capabilities:max_hash_alg for notifying the controller.

Comment 2 Aaron Conole 2023-07-11 13:03:09 UTC
As Comment 1 notes, this feature already exists for advertising the correct hash.