netdev - Re: Question on Lockless TX

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Message-ID: <CA+mtBx-m2zZfZ3AQOkv=4St2bWpipEEY0+O7kAJtReCa6ZkizA@mail.gmail.com>
Date:	Wed, 16 Apr 2014 09:51:09 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Sharat Masetty <sharat04@...il.com>
Cc:	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: Question on Lockless TX

On Tue, Apr 15, 2014 at 9:29 PM, Sharat Masetty <sharat04@...il.com> wrote:
> Can someone explain to me, why would a driver choose to implement
> Lockless TX? What are the advantages/disadvantages of choosing to do
> so?Any performance benefits? A reference to a sample driver
> implementation would be helpful to understand.
>
Locks in the TX path are needed provide mutual exclusion to the
underlying HW queue and other structures. Some drivers either don't
need any form of locking because their is no queue to protect (often
the case with virtual drivers like loopback and bonding), others might
provide their own locking at higher granularity or for other purposes.
Generally, taking fewer locks can reduce lock contention, atomic
operations, and cache line misses. If you grep for NETIF_F_LLTX under
drivers/net you can find examples of drivers that support this. Also,
please look at Documentation/networking/netdevices.txt.

Tom

> Thanks
> Sharat
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