From: Krishna Kumar <krkumar2@in•ibm.com>
To: johnpol@2ka•mipt.ru, herbert@gondor•apana.org.au,
hadi@cyberus•ca, kaber@trash•net,
shemminger@linux-foundation•org, davem@davemloft•net
Cc: jagana@us•ibm.com, Robert.Olsson@data•slu.se,
peter.p.waskiewicz.jr@intel•com, kumarkr@linux•ibm.com,
xma@us•ibm.com, gaagaan@gmail•com, netdev@vger•kernel.org,
rdreier@cisco•com, rick.jones2@hp•com, mcarlson@broadcom•com,
jeff@garzik•org, general@lists•openfabrics.org,
mchan@broadcom•com, tgraf@suug•ch,
Krishna Kumar <krkumar2@in•ibm.com>,
sri@us•ibm.com
Subject: [PATCH 1/10 Rev4] [Doc] HOWTO Documentation for batching
Date: Wed, 22 Aug 2007 13:58:58 +0530 [thread overview]
Message-ID: <20070822082858.11964.87377.sendpatchset@localhost.localdomain> (raw)
In-Reply-To: <20070822082839.11964.63503.sendpatchset@localhost.localdomain>
Add Documentation describing batching skb xmit capability.
Signed-off-by: Krishna Kumar <krkumar2@in•ibm.com>
---
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
+ driver to use this capability is that it should have a reasonably
+ 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
+ transmit it immediately (via qdisc_run). However, events like tx lock
+ contention, tx queue stopped, etc, can result in the skb not getting
+ 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
+ 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
+ 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.
next prev parent reply other threads:[~2007-08-22 8:27 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-22 8:28 [PATCH 0/10 Rev4] Implement skb batching and support in IPoIB Krishna Kumar
2007-08-22 8:28 ` Krishna Kumar [this message]
2007-08-22 15:50 ` [ofa-general] Re: [PATCH 1/10 Rev4] [Doc] HOWTO Documentation for batching Randy Dunlap
2007-08-23 2:48 ` Krishna Kumar2
2007-08-22 8:29 ` [PATCH 2/10 Rev4] [core] Add skb_blist & support " Krishna Kumar
2007-08-22 8:29 ` [PATCH 3/10 Rev4] [sched] Modify qdisc_run to support batching Krishna Kumar
2007-08-22 8:29 ` [PATCH 4/10 Rev4] [ethtool] Add ethtool support Krishna Kumar
2007-08-22 8:30 ` [PATCH 5/10 Rev4] [IPoIB] Header file changes Krishna Kumar
2007-08-22 8:30 ` [PATCH 6/10 Rev4] [IPoIB] CM & Multicast changes Krishna Kumar
2007-08-22 8:30 ` [PATCH 7/10 Rev4] [IPoIB] Verbs changes Krishna Kumar
2007-08-22 8:31 ` [PATCH 8/10 Rev4] [IPoIB] Post and work completion handler changes Krishna Kumar
2007-08-22 8:31 ` [PATCH 9/10 Rev4] [IPoIB] Implement batching Krishna Kumar
2007-08-22 8:31 ` [PATCH 10/10 Rev4] [E1000] " Krishna Kumar
2007-08-22 14:39 ` [ofa-general] " Kok, Auke
2007-08-23 2:44 ` Krishna Kumar2
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