Hi Randy, Thanks for your suggestions. Will clean up those changes.
- KK Randy Dunlap <[EMAIL PROTECTED]> wrote on 08/22/2007 09:20:13 PM: > On Wed, 22 Aug 2007 13:58:58 +0530 Krishna Kumar wrote: > > > Add Documentation describing batching skb xmit capability. > > > > Signed-off-by: Krishna Kumar <[EMAIL PROTECTED]> > > --- > > batching_skb_xmit.txt | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 files changed, 78 insertions(+) > > > > diff -ruNp org/Documentation/networking/batching_skb_xmit.txt > new/Documentation/networking/batching_skb_xmit.txt > > --- org/Documentation/networking/batching_skb_xmit.txt 1970-01-01 05:30: > 00.000000000 +0530 > > +++ new/Documentation/networking/batching_skb_xmit.txt 2007-08-22 10:21: > 19.000000000 +0530 > > @@ -0,0 +1,78 @@ > > + HOWTO for batching skb xmit support > > + ----------------------------------- > > + > > +Section 1: What is batching skb xmit > > +Section 2: How batching xmit works vs the regular xmit > > +Section 3: How drivers can support batching > > +Section 4: How users can work with batching > > + > > + > > +Introduction: Kernel support for batching skb > > +---------------------------------------------- > > + > > +A new capability to support xmit of multiple skbs is provided in the netdevice > > +layer. Drivers which enable this capability should be able to process multiple > > +skbs in a single call to their xmit handler. > > + > > + > > +Section 1: What is batching skb xmit > > +------------------------------------- > > + > > + This capability is optionally enabled by a driver by setting the > > + NETIF_F_BATCH_SKBS bit in dev->features. The pre-requisite for a > > prerequisite > > > + driver to use this capability is that it should have a reasonably > > I would say "reasonably-sized". > > > + sized hardware queue that can process multiple skbs. > > + > > + > > +Section 2: How batching xmit works vs the regular xmit > > +------------------------------------------------------- > > + > > + The network stack gets called from upper layer protocols with a single > > + skb to transmit. This skb is first enqueue'd and an attempt is made to > > enqueued > > > + transmit it immediately (via qdisc_run). However, events like tx lock > > + contention, tx queue stopped, etc, can result in the skb not getting > > etc., > > > + sent out and it remains in the queue. When the next xmit is called or > > + when the queue is re-enabled, qdisc_run could potentially find > > + multiple packets in the queue, and iteratively send them all out > > + one-by-one. > > + > > + Batching skb xmit is a mechanism to exploit this situation where all > > + skbs can be passed in one shot to the device. This reduces driver > > + processing, locking at the driver (or in stack for ~LLTX drivers) > > + gets amortized over multiple skbs, and in case of specific drivers > > + where every xmit results in a completion processing (like IPoIB) - > > + optimizations can be made in the driver to request a completion for > > + only the last skb that was sent which results in saving interrupts > > + for every (but the last) skb that was sent in the same batch. > > + > > + Batching can result in significant performance gains for systems that > > + have multiple data stream paths over the same network interface card. > > + > > + > > +Section 3: How drivers can support batching > > +--------------------------------------------- > > + > > + Batching requires the driver to set the NETIF_F_BATCH_SKBS bit in > > + dev->features. > > + > > + The driver's xmit handler should be modified to process multiple skbs > > + instead of one skb. The driver's xmit handler is called either with a > > an > > > + skb to transmit or NULL skb, where the latter case should be handled > > + as a call to xmit multiple skbs. This is done by sending out all skbs > > + in the dev->skb_blist list (where it was added by the core stack). > > + > > + > > +Section 4: How users can work with batching > > +--------------------------------------------- > > + > > + Batching can be disabled for a particular device, e.g. on desktop > > + systems if only one stream of network activity for that device is > > + taking place, since performance could be slightly affected due to > > + extra processing that batching adds (unless packets are getting > > + sent fast resulting in stopped queue's). Batching can be enabled if > > queues). > > > + more than one stream of network activity per device is being done, > > + e.g. on servers; or even desktop usage with multiple browser, chat, > > + file transfer sessions, etc. > > + > > + Per device batching can be enabled/disabled by passing 'on' or 'off' > > + respectively to ethtool. > > with what other parameter(s), e.g., > > ethtool <dev> batching on/off ? > > --- > ~Randy > *** Remember to use Documentation/SubmitChecklist when testing your code *** - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
