在 2023/2/24 下午4:13, Michael S. Tsirkin 写道:
On Thu, Feb 23, 2023 at 02:40:46PM +0000, Parav Pandit wrote:
From: Michael S. Tsirkin <m...@redhat.com>
Sent: Thursday, February 23, 2023 8:14 AM
On Sat, Feb 18, 2023 at 10:37:15PM +0800, Heng Qi wrote:
So for RSS specifically, we brain-stormed with Amnon (Cc'd) and came up with
an idea: RSS indirection table entries are 16 bit but onlu 15 bits are used to
indentify an RX queue.
We can use the remaining bit as a "tunnel bit" to signal whether to use the
inner or the outer hash for queue selection.
I further brainstormed internally with Saeed and Rony on this.
The inner hash is only needed for GRE, IPIP etc.
For VXLAN and NVGRE Linux kernel transmit side uses the entropy of the source
port of the outer header.
It does that based on the inner header.
Refer to [1] as one example.
[1] https://elixir.bootlin.com/linux/latest/source/drivers/net/geneve.c#L922
But I think hash was requested for RSS with dpdk, no?
I think yes, at least probably the first customer to use the feature
might be dpdk.:)
The lookup will work like this then:
calculate outer hash
if (rss[outer hash] & tunnel bit)
Tunnel bit, you mean tunneled packet, right?
this idea stores a bit in the indirection table
which signals which of the hashes to use for rss
This allows inner hash to have the ability to select a queue and place
packets to the queue (that is, parallel to RSS),
which seems to be different from our discussion before v9. 🙁
Thanks.
then
calculate inner hash
return rss[inner hash] & ~tunnel bit
Why to end with a tunnel bit?
this just clears the bit so we end up with a vq number.
else
return rss[outer hash]
this fixes the security issue returning us back to status quo : specific
tunnels can
be directed to separate queues.
The number of tunnels is far higher than the number of queues with para virt
driver doing decap.
True. This seeks to get us back to where we are before the feature:
driver can send specific outer hashes to specific queues.
outer hash collisions remain a problem.
This is for RSS.
For hash reporting indirection table is not used.
Maybe it is enough to signal to driver that inner hash was used.
We do need that signalling though.
My question would be whether it's practical to implement in hardware.
In above example, hw calculating double hash is difficult without much gain.
Either calculating on one inner or outer makes sense.
Signaling whether calculated on inner or outer is fine because hw exactly tells
what it did.
This, in a sense, is what reporting hash tunnel type did.
Do you now think we need it?
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