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
