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SubjectRe: 3x slower file reading oddity
On Mon, 17 Jun 2002, Benjamin LaHaise wrote:

> On Mon, Jun 17, 2002 at 01:03:15PM -0700, dean gaudet wrote:
> > 3x slower with the two cats in parallel.
>
> cat uses an incredibly small buffer for file io (4KB on x86), so
> running multiple cats in parallel will simply thrash your disk.
> What you really want is to run the open()s in parallel and the
> read()s sequentially (or in parallel with a large buffer to cut
> down on the seek cost).

using a 64KB buffer makes the xargs -P2 only twice as long as the -P1 ...
so that's an improvement, but still something seems odd. (btw, many of
the files are tiny anyhow -- a bunch of maildirs mixed in amongst the
files.)

i'll try playing around with threading the open()s.

-dean

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