Re: [hybi] frame length encoding

[Patrick McManus <[e-mail]>]

On Sat, 2010-08-21 at 16:59 -0400, John Tamplin wrote:
> On Sat, Aug 21, 2010 at 4:57 PM, Shelby Moore <[e-mail]>
> wrote:

>          Can you simply rewrite
>         one sector on disk and the memory manager remaps?
> 
> 
> I haven't tried it personally, but I would suspect you could use
> TCP_CORK, write a header, use sendfile to send a chunk of the file to
> finish the frame, uncork, repeat until done.  I don't think there
> would be any extra copying involved here, but you can't just issue the
> sendfile and go on to the next message, you need some thread that will
> queue up the next frame when it is ready.

That is correct (and I have done this personally), you need multiple
calls of the ZC API interleaved with the write of the chunk header.
There is no copying of the data through the CPU just because it requires
multiple calls. And there is no reason you couldn't implement some kind
of writev() like API that lets you interleave copied and zero-copied
data.

And yes, multiple calls are more overhead than 1 call. but at 1 per 4GB,
it really is inconsequential.