netdev - Re: interrupt coalescing and CSUM offload

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Message-ID: <20120914093252.020992cc@nehalam.linuxnetplumber.net>
Date:	Fri, 14 Sep 2012 09:32:52 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
Cc:	netdev@...r.kernel.org
Subject: Re: interrupt coalescing and CSUM offload

On Fri, 14 Sep 2012 16:35:13 +0200
Joakim Tjernlund <joakim.tjernlund@...nsmode.se> wrote:

> 
> I am adding interrupt coalescing to the ucc_geth driver. Unfortunately
> there is only support for RX interrupt coalescing.
> I wonder if there is any way "simulate" TX interrupt coalescing?
> 
> I am also looking at adding HWCSUM support but this device can only do
> IP header CSUM offload. This doesn't seem to be an option in Linux?
> As I understand it, one must do CSUM offload for the whole frame, both
> IP header and TCP/UDP csums?
> 
>  Jocke

There are a few drivers that turn off TX interrupt completely.
They cleanup TX buffers on next send and have a timer to cleanup
as well. This has performance benefits, but it does cause issues
with local flow control (the freeing of skb is used to rate
limit local traffic).

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