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

Gérard Roudier
2001-08-25T09:16:13Z

On Sat, 25 Aug 2001, Rik van Riel wrote:

> On Sat, 25 Aug 2001, Marc A. Lehmann wrote:
> > On Fri, Aug 24, 2001 at 05:19:07PM -0300, Rik van Riel <riel@conectiva.com.br> wrote:
> > > Actually, no. FIFO would be ok if you had ONE readahead
> > > stream going on, but when you have multiple readahead
> >
> > Do we all agree that read-ahead is actually the problem? ATM, I serve
> > ~800 files, read()ing them in turn. When I increase the number of
> > threads I have more reads at the same time in the kernel, but the
> > absolute number of read() requests decreases.
>
> [snip evidence beyond all doubt]

I am not so sure. :)

Btw, the new VM and elevator have been very long to stabilize. Such
erratic development process does not make softwares appear trustable to
me. I would also suspect some flaws in these parts, too.

> Earlier today some talking between VM developers resulted
> in us agreeing on trying to fix this problem by implementing
> dynamic window scaling for readahead, using heuristics not
> all that much different from TCP window scaling.

It is probably time to rewrite this old code. Good luck for that.

> This should make the system able to withstand a higher load
> than currently, while also allowing fast data streams to
> work with more efficiently than currently.

That's the wish. Just crossing finger for things to work a lot better than
the development of your new VM and elevator improvements. :-)

Regards,
Gérard.