netdev - Re: [WIP][PATCHES] Network xmit batching

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Date:	Wed, 4 Jul 2007 09:49:32 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	hadi@...erus.ca
Cc:	David Miller <davem@...emloft.net>,
	Gagan Arneja <gaagaan@...il.com>,
	Jeff Garzik <jeff@...zik.org>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Matt Carlson <mcarlson@...adcom.com>,
	Michael Chan <mchan@...adcom.com>,
	netdev <netdev@...r.kernel.org>, Rick Jones <rick.jones2@...com>,
	Robert Olsson <Robert.Olsson@...a.slu.se>,
	Sridhar Samudrala <sri@...ibm.com>
Subject: Re: [WIP][PATCHES] Network xmit batching - tg3 support

Hi Jamal,

J Hadi Salim <j.hadi123@...il.com> wrote on 07/03/2007 06:56:20 PM:

> On Mon, 2007-02-07 at 17:21 -0700, Michael Chan wrote:
>
> [Matt, please include the count in the fix per previous email]
> long answer:
> My goal with storing these values and computing them was to do certain
> things that dont require holding the netif_tx_lock within a batch as
> well. Evaluating the packet metadata and formating the packet to be
> ready for stashing into DMA was one thing i could do outside of holding
> the lock easily - and running that in loop of 100 packets amortizes the
> instruction cache and allows me (when i get to it) to hold the lock for
> a lot less computation.

Do you see any contention for tx_lock which can justify having a prep
handler? As I understood, no other CPU can be in the xmit code at the
same time since RUNNING bit is held. Hence getting this lock early or
late should not matter for the xmit side (and you are also holding
dev->queue_lock while running prep so no new skbs can also be added to
the dev during this time). And I couldn't find any driver that uses the
same tx_lock on rx, so where is the saving by doing prep ?

- KK

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