Re: Known problems with dcache?

Daniel Jacobowitz
2003-01-10T22:38:22Z

On Fri, Jan 10, 2003 at 05:35:56PM -0500, Andrew Cagney wrote:
>
> >We don't use the straw on some targets now; Linux (need to get back to
> >that patch and turn it on always!), *BSD.
>
> Right so that 32 byte read is now cheap.
>
> >The dcache needs some serious work if you want it to be always on.
> >Last time I tested it it caused an actual slowdown. Basically, it's
> >too small to be useful.
> >
> >#define DCACHE_SIZE 64
> >#define LINE_SIZE_POWER (5)
> >
> >So it never stores more than 2K. LinuxThreads _overwhelms_ that, by a
> >downright boggling amount.
>
> You wouldn't know why it caused a slow down? Th 32 byte read should now
> be cheaper.

This was before the 32-byte-read support. So we read lines in, did
more computation than before, and overwrote them in the cache; exactly
the same I/O, more CPU. Might be worth trying it again, with larger
lines, now. Not sure.

--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer