netdev - Re: [PATCH] Implementation of the sendgroup() system call

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Message-ID: <20090504145046.GI23223@one.firstfloor.org>
Date:	Mon, 4 May 2009 16:50:46 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Elad Lahav <elahav@...uwaterloo.ca>
Cc:	Andi Kleen <andi@...stfloor.org>, Elad Lahav <elahav@...terloo.ca>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Implementation of the sendgroup() system call

On Mon, May 04, 2009 at 09:44:31AM -0400, Elad Lahav wrote:
> >My guess it's more the copies than the calls?
> It's a factor of both. This is why we also created the sendgroup()  
> implementation that uses a tight loop of in-kernel calls to sendmsg()  
> as a means for evaluating the cost of mode switches. It is definitely  
> not negligible (exact numbers depend on the size of the group and the  
> size of the payload, of course).

How much is non negligible in your case?

> 
> >It sounds like you want sendfile() for UDP.
> Do you mean by having a per-recipient sendfile() call for the same  
> file? Leaving the cost of the system call aside, this solution does  
> not work well with the kind of real-time data that we've been working  
> with (live streaming, online games). You would have to write the  
> payload to the file as it is being generated and call sendfile() after  
> each such write.

You can mmap the file.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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