On Thu, Jun 07, 2007 at 06:23:16PM -0400, jamal ([EMAIL PROTECTED]) wrote:
> On Thu, 2007-07-06 at 20:13 +0400, Evgeniy Polyakov wrote:
>
> > Actually I wonder where the devil lives, but I do not see how that
> > patchset can improve sending situation.
> > Let me clarify: there are two possibilities to send data:
> > 1. via batched sending, which runs via queue of packets and performs
> > prepare call (which only setups some private flags, no work with
> > hardware) and then sending call.
>
> I believe both are called with no lock. The idea is to avoid the lock
> entirely when unneeded. That code may end up finding that the packet
> is bogus and throw it out when it deems it useless.
> If you followed the discussions on multi-ring, this call is where
> i suggested to select the tx ring as well.
Hmm...
+ netif_tx_lock_bh(odev);
+ if (!netif_queue_stopped(odev)) {
+
+ idle_start = getCurUs();
+ pkt_dev->tx_entered++;
+ ret = odev->hard_batch_xmit(&odev->blist, odev);
+ if (!spin_trylock_irqsave(&tx_ring->tx_lock, flags)) {
+ /* Collision - tell upper layer to requeue */
+ return NETDEV_TX_LOCKED;
+ }
+
+ while ((skb = __skb_dequeue(list)) != NULL) {
+#ifdef coredoesnoprep
+ ret = netdev->hard_prep_xmit(skb, netdev);
+ if (ret != NETDEV_TX_OK)
+ continue;
+#endif
+
+ /*XXX: This may be an opportunity to not give nit
+ * the packet if the dev ix TX BUSY ;-> */
+ dev_do_xmit_nit(skb, netdev);
+ ret = e1000_queue_frame(skb, netdev);
The same applies to *_gso case.
> > 2. old xmit function (which seems to be unused by kernel now?)
> >
>
> You can change that by turning off _BTX feature in the driver.
> For WIP reasons it is on at the moment.
>
> > Btw, prep_queue_frame seems to be always called under tx_lock, but it
> > old e1000 xmit function calls it without lock.
>
> I think both call it without lock.
Without lock that would be wrong - it accesses hardware.
> > Locked case is correct,
> > since it accesses private registers via e1000_transfer_dhcp_info() for
> > some adapters.
>
> I am unsure about the value of that lock (refer to email to Auke). There
> is only one CPU that can enter the tx path and the contention is
> minimal.
>
> > So, essentially batched sending is
> > lock
> > while ((skb = dequue))
> > send
> > unlock
> >
> > where queue of skbs are prepared by stack using the same transmit lock.
> >
> > Where is a gain?
>
> The amortizing of the lock on tx is where the value is.
> Did you see the numbers Evgeniy? ;->
> Heres one i can vouch on a dual processor 2GHz that i tested with
> pktgen;
I only saw results Krishna posted, and i also do not know, what
service demand is :)
> ----
> 1) Original e1000 driver (no batching):
> a) We got a xmit throughput of 362Kpackets/second of 362K with
> the default setup (everything falls on cpu#0).
> b) With tying to CPU#1, i saw 401Kpps.
>
> 2) Repeated the tests with batching patches (as in this commit)
> And got an outstanding 694Kpps throughput.
>
> 5) Repeated #4 with binding to cpu #1.
> And throughput didnt improve that much - was hitting 697Kpps
> I think we are pretty much hitting upper limits here
> ...
> ----
>
> I am actually testing as we speak on faster hardware - I will post
> results shortly.
Result looks good, but I still do not understand how it appeared, that
is why I'm not that excited about idea - I just do not know it in
details.
--
Evgeniy Polyakov
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