From: Stephen Hemminger <shemminger@vyatta.com>
To: Tom Herbert <therbert@google.com>
Cc: davem@davemloft.net, netdev@vger.kernel.org
Subject: Re: [PATCH 1/2] net: Allow no-cache copy from user on transmit
Date: Tue, 8 Mar 2011 22:12:52 -0800 [thread overview]
Message-ID: <20110308221252.34385919@s6510> (raw)
In-Reply-To: <alpine.DEB.2.00.1103082053350.1433@pokey.mtv.corp.google.com>
On Tue, 8 Mar 2011 21:05:06 -0800 (PST)
Tom Herbert <therbert@google.com> wrote:
> This patch uses __copy_from_user_nocache (from skb_copy_to_page)
> on transmit to bypass data cache for a performance improvement.
> This functionality is configurable per device using ethtool, the
> device must also be doing TX csum offload to enable. It seems
> reasonable to set this when the device does not copy or
> otherwise touch the data.
>
> This patch was tested using 200 instances of netperf TCP_RR with
> 1400 byte request and one byte reply. Platform is 16 core AMD.
>
> No-cache copy disabled:
> 672703 tps, 97.13% client utilization
> 50/90/99% latency 244.31 484.205 1028.41
>
> No-cache copy enabled:
> 702113 tps, 96.16% client utilization,
> 50/90/99% latency 238.56 467.56 956.955
>
> This seems to provide a nice little performance improvement and is
> consistent in the tests I ran. Presumably, this would provide
> the greatest benfits in the presence of an application workload
> stressing the cache and a lot of transmit data happening. I don't
> yet see a downside to using this.
>
> Signed-off-by: Tom Herbert <therbert@google.com>
Since this is not an ethernet only optimization or device
specific, I would prefer it be a property of device not
something in ethtool.
next prev parent reply other threads:[~2011-03-09 6:12 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-09 5:05 [PATCH 1/2] net: Allow no-cache copy from user on transmit Tom Herbert
2011-03-09 6:12 ` Stephen Hemminger [this message]
2011-03-09 13:04 ` Michał Mirosław
2011-03-09 19:18 ` Tom Herbert
2011-03-09 19:38 ` Ben Hutchings
2011-03-09 19:51 ` Michał Mirosław
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