On 7/13/15 1:04 PM, David Miller wrote:
From: Alexei Starovoitov <a...@plumgrid.com>
Date: Mon, 13 Jul 2015 12:47:42 -0700
In all normal cases skb->users == 1, but pktgen is using trick:
atomic_add(burst, &skb->users);
so when testing something like:
You can want pktgen rx (which is the only buggy case as far as I can
see, TX is fine) to run fast, but you must do so by abiding by the
appropriate SKB sharing rules.
You can't do an optimization in pktgen for RX processing that works
"some of the time". We have shared SKB rules for a reason.
And I don't want to have to explain to someone in the future why that
drop check is there, and have to tell them "because pktgen is broken
and we decided to add a hack here rather than make pktgen send
properly formed SKBs into the RX path"
Ok?
in general all makes sense, but it is both RX and TX.
Without burst hack we cannot achieve line rate TX.
atomic_add(burst, &pkt_dev->skb->users);
xmit_more:
ret = netdev_start_xmit(pkt_dev->skb, odev, txq, --burst > 0);
in pktgen we check that driver can work with users > 1 via:
pkt_dev->odev->priv_flags & IFF_TX_SKB_SHARING
so real hw driver are mostly ready for users > 1, it's only
few tc actions struggle a bit.
We cannot check tc actions from pktgen, since they can be added
dynamically.
So I see three options:
1 get rid of burst hack for both RX and TX in pktgen (kills performance)
2 add unlikely(skb_shread) check to few tc actions
3 do nothing
I think 2 isn't that bad after all if properly documented with
"because pktgen is doing this hack for performance" ?
I'm fine with 3 too, since the whole pktgen business is for root
and for kernel hackers who suppose to know what they're doing.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
