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List:       linux-nfs
Subject:    Re: [NFS] 8K limit still there?
From:       Tom McNeal <mcneal () mclinux ! com>
Date:       2001-10-19 16:55:06
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I believe this is one of the causes of non-uniform performance 
patterns when HP was reviewing the move to 32K in HP-UX,  but it 
made a big difference with large file transfers (assuming less 
random IO, which probably isn't such a good assumption).  I've 
installed a 2.4.12 kernel here with 32K limits, and I've got a 
couple vendor platforms to talk to, so I'll get back to the mailing 
list next week.

Tom McNeal


Trond Myklebust wrote:
> 
> >>>>> " " == Craig I Hagan <hagan@cih.com> writes:
> 
>     >> socket keeps returning -EAGAIN.  IOW I'd expect you'd in fact
>     >> see a heavy performance drop when doing block reads against
>     >> such a server...
> 
>      > I was seeing slightly improved performance using larger blocks,
>      > however, the network i was using was fully switched and faster
>      > than the server could sent at. I saw a good percentage of wire
>      > speed gigE doing sequential reads from a client of a file
>      > larger than server and clients's ram.
> 
> For Gigabit nets that's probably true, but ordinary switched 100Mbit
> will quickly choke up. Don't forget that, the default buffer size on
> sockets is 64k, so all you need is for two 32k read requests to be
> processed simultaneously in order to fill up beyond your socket buffer
> capacity (your replies are >32k due to RPC overhead).
> 
> That's why the client goes to such lengths in net/sunrpc/xprt.c to
> hook the write_space() socket callback, etc...
> 
> Cheers,
>   Trond

-- 
----------------------------------------------------------
Tom McNeal                              mcneal@mclinux.com
Director of Engineering & Operations, West Coast Office
Mission Critical Linux, Inc.
1333 Lawrence Expressway, Suite 438, Santa Clara, CA 95051
Phone: 408-615-9100 x201                Fax:  408-615-9105
----------------------------------------------------------

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