Messages in this thread | | | Date | Sun, 25 Apr 1999 23:32:24 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: bad lmbench numbers for mmap |
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On Sun, 25 Apr 1999, Larry McVoy wrote: > > So do you want me to change it to do reads instead?
Yes.
But save the old version away as a "lat_mmap_write" or something.
Btw, you need to fix lat_mmap anyway: right now the summary information gives random numbers that depend on how large an area the user asked you to use. So you can't compare lat_mmap by looking at the summary stuff, which kind of defeats having a summary in the first place.
I'd suggest taking the 1MB (or some other fixed size) number into the summary.
> Another thing I could do is to factor out the cost of mmap by running two > experiments: > > a) repeatedly read a region which is already mapped > > b) repeatedly mmap & read & unmap. > > In theory, b - a == mmap+munmap cost. However, if the munmap causes the > caches to get flushed, or if the new mapping is somewhere else, then cache > misses start skewing the results.
I don't think it should much matter. But I don't have any numbers, so..
Linus
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