Re: [resent PATCH] Re: very slow parallel read performance

Daniel Phillips
2001-08-26T16:48:40Z

On August 25, 2001 01:23 am, pcg@goof.com ( Marc) (A.) (Lehmann ) wrote:
> I could imagine that read() executes, returns to
> userspace and at the same time the kernel thinks "nothing to do, let's
> readahead". While, in the concurrent case, there is hardly a time when no
> read() is running. But read-ahead does not seem to work that way.

But it's a very interesting idea: instead of performing readahead in
generic_file_read the user thread would calculate the readahead window
information and pass it off to a kernel thread dedicated to readahead.
This thread can make an informed, global decision on how much IO to
submit. The user thread benefits by avoiding some stalls due to
readahead->readpage, as well as avoiding thrashing due to excessive
readahead.

--
Daniel