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

Lehmann
2001-08-26T13:22:20Z

On Sun, Aug 26, 2001 at 12:32:09AM -0300, Rik van Riel <riel@conectiva.com.br> wrote:
> Reality check time indeed. If you propose that disabling
> readahead should improve read performance something fishy
> is going on ;)

Actually, I also believe that. If you have no memory to store read-ahead
data then your only chance is what I try to do: massively parallelize
reads so the elevator can optimize what's possible and do no read-ahead
whatsoever.

Of course, in general, read-ahead is a must. Using 256k socket buffer
+ 128k userspace bounce buffer is, effectively, a 384k read-ahead per
connenction (the average connection speed is about 8k/s btw, so thats
about one read every 16 seconds. 16 seconds is also about the time between
sending out the response headers and the beginning of the data transfer,
which is ok in my case). The problem is that read-ahead (seems to) go
completely havoc when read()'s are issued in many threads at the same time.

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