On Fri, Jun 08, 2007 at 07:31:07AM -0400, jamal (hadi@cyberus.ca) wrote:

On Fri, 2007-08-06 at 12:38 +0400, Evgeniy Polyakov wrote:

quoted

On Thu, Jun 07, 2007 at 06:23:16PM -0400, jamal (hadi@cyberus.ca) wrote:

quoted

quoted

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

[..]

quoted

+	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);

[..]

quoted

The same applies to *_gso case.

You missed an important piece which is grabbing of
__LINK_STATE_QDISC_RUNNING

But lock is still being hold - or there was no intention to reduce lock
usage? As far as I read Krishna's mail, lock usage was not an issue, so
that hunk probably should be dropped from the analysis.
 

quoted

Without lock that would be wrong - it accesses hardware.

We are achieving the goal of only a single CPU entering that path. Are
you saying that is not good enough?

Then why essentially the same code (current batch_xmit callback)
previously was always called with disabled interrupts? Aren't there
some watchdog/link/poll/whatever issues present?

quoted

and i also do not know, what service demand is :)

From the explanation seems to be how much cpu was used while sending. Do
you have any suggestions for computing cpu use?
in pktgen i added code to count how many microsecs were used in
transmitting.

Something, that anyone can understand :)
For example /proc stats, although it is not very accurate, but it is
really usable parameter from userspace point ov view.

quoted

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.

To add to KKs explanation on other email:
Essentially the value is in amortizing the cost of barriers and IO per
packet. For example the queue lock is held/released only once per X
packets. DMA kicking which includes both a PCI IO write and mbs is done
only once per X packets. There are still a lot of room for improvement
of such IO;

Btw, what is the size of the packet in pktgen in your tests? Likely it
is small, since result is that good. That can explain alot.

cheers,
jamal

-- 
	Evgeniy Polyakov