Subject: Re: [PATCH v2] socket.7: add description for SO_BUSY_POLL

From: Michael Kerrisk <[email-masked]>
Date: Wed, 10 Jul 2013 20:03:08 +0200

On 07/10/13 16:18, Eliezer Tamir wrote:
> Add description for the SO_BUSY_POLL socket option to the socket(7) manpage.
> 
> v2
> fixed typos reported by Rasmus Villemoes

Eliezer,

What's the status of this feature. A quick grep seems to show
that the feature is not yet in mainline. What is the plan?

Thanks,

Michael

> Signed-off-by: Eliezer Tamir <[email-masked]>
> ---
> 
>  man7/socket.7 |   25 +++++++++++++++++++++++++
>  1 files changed, 25 insertions(+), 0 deletions(-)
> 
> diff --git a/man7/socket.7 b/man7/socket.7
> index f2213eb..5edcb09 100644
> --- a/man7/socket.7
> +++ b/man7/socket.7
> @@ -694,6 +694,31 @@ for details on control messages.
>  Gets the socket type as an integer (e.g.,
>  .BR SOCK_STREAM ).
>  This socket option is read-only.
> +.TP
> +.B SO_BUSY_POLL
> +Sets the approximate time in microseconds to busy poll on a blocking receive
> +when there is no data. Increasing this value requires
> +.BR CAP_NET_ADMIN . 
> +The default for this option is controlled by the
> +.I /proc/sys/net/core/busy_read
> +file. 
> +
> +The value in the  
> +.I /proc/sys/net/core/busy_poll
> +file determines how long 
> +.BR select (2)
> +and 
> +.BR poll (2)
> +will busy poll when they operate on sockets with 
> +.BR SO_BUSY_POLL
> +set and no events to report are found.
> +
> +In both cases busy polling will only be done when the socket last received data
> +from a network device that supports this option.
> +
> +While busy polling may improve latency of some applications, care must be
> +taken when using it since this will increase both CPU utilization and power usage.
> +
>  .SS Signals
>  When writing onto a connection-oriented socket that has been shut down
>  (by the local or the remote end)
> 
>