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Re: Known problems with dcache?


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.
Well, possibly more I/O. And, I think, the I/O / context switch / ... is the expensive part.

  Might be worth trying it again, with larger
lines, now.  Not sure.
Was it on an i386? If it was, the other other cache would easily skew any results.

Andrew




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