Re: Garbage collection

On 15 Aug 2004 22:16:47 -0400, glen herrmannsfeldt <gah@ugcs.caltech.edu>
wrote:


>>> There is a story of someone testing the cache memory
>>> characteristics of a machine with C code like:
>
>>> int *a,*b,i;
>>> a=malloc(100000000);
>>> b=malloc(100000000);
>>> for(i=0;i<100000000;i++) a[i]=b[i];
>
>>> It would seem that this would require moving enough data to
>>> completely flush the cache, but it might not.
>
>> An interesting test, but not really a fair test of a machine's
>> speed, since it is somewhat unrepresentative of real workloads.
>
> You mean moving 1e8 bytes isn't fair, or copying the same
> page many times, inside the cache?


I didn't mean copying the same page many times, since I didn't
realise that was what the above code would do (it presumably would
while reading the b array, under the regime you mention).


I simply meant that copying a very large (100 MB?) linear chunk of
memory is not a fair test of a machine's speed, because real
applications will very rarely do this (I'm sure it will be done
occasionally, but not very often).


I understand that one measure made by suites designed to
realistically test out the performance of a machine is of a very
large number of small block moves, say 50 bytes each, spread around
an assumed working set of 10 to 20 MB.


--
Nick Roberts

Return to the comp.compilers page.
Search the comp.compilers archives again.