Re: sendfile+zerocopy: fairly sexy (nothing to do with ECN)

From: David Lang (
Date: Fri Feb 02 2001 - 17:57:42 EST

Thanks, that info on sendfile makes sense for the fileserver situation.
for webservers we will have to see (many/most CGI's look at stuff from the
client so I still have doubts as to how much use cacheing will be)

David Lang

On Fri, 2 Feb 2001, David S. Miller wrote:

> Date: Fri, 2 Feb 2001 14:46:07 -0800 (PST)
> From: David S. Miller <>
> To: David Lang <>
> Cc: Andrew Morton <>, lkml <>,
> "" <>
> Subject: Re: sendfile+zerocopy: fairly sexy (nothing to do with ECN)
> David Lang writes:
> > 1a. for webservers that server static content (and can therefor use
> > sendfile) I don't see this as significant becouse as your tests have been
> > showing, even a modest machine can saturate your network (unless you are
> > useing gigE at which time it takes a skightly larger machine)
> Start using more than one interface, then it begins to become
> interesting.
> > 1b. for webservers that are not primarily serving static content, they
> > have to use write() for the output from cgi's, etc and therefor pay the
> > performance penalty without being able to use sendfile() much to get the
> > advantages. These machines are the ones that really need the performance
> > as the cgi's take a significant amount of your cpu.
> CGI's can be cached btw if the implementation is clever (f.e. CGI
> tells the web server that if the file used as input to the CGI does
> not change then the output from the CGI will not change, meaning CGI
> output is based solely on input, therefore CGI output can be cached
> by the web server).
> > 2. for other fileservers sendfile() sounds like it would be useful if the
> > client is reading the entire file, but what about the cases where the
> > client is reading part of the file, or is writing to the file. In both of
> > these cases it seems that the fileserver is back to the write() penalty.
> > does anyone have stats on the types of requests that fileservers are being
> > asked for?
> It helps no matter what part of the file the client reads.
> sendfile() can be used on an arbitrary offset+len portion of
> a file, it is not limited to just sending an entire fire.
> Later,
> David S. Miller
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