On Thu, 2011-09-15 at 14:24 -0500, Seth Jennings wrote: > How would you suggest that I measure xcfmalloc performance on a "very > large set of workloads". I guess another form of that question is: How > did xvmalloc do this? Well, it didn't have a competitor, so this probably wasn't done. :) I'd like to see a microbenchmarky sort of thing. Do a million (or 100 million, whatever) allocations, and time it for both allocators doing the same thing. You just need to do the *same* allocations for both. It'd be interesting to see the shape of a graph if you did: for (i = 0; i < BIG_NUMBER; i++) for (j = MIN_ALLOC; j < MAX_ALLOC; j += BLOCK_SIZE) alloc(j); free(); ... basically for both allocators. Let's see how the graphs look. You could do it a lot of different ways: alloc all, then free all, or alloc one free one, etc... Maybe it will surprise us. Maybe the page allocator overhead will dominate _everything_, and we won't even see the x*malloc() functions show up. The other thing that's important is to think of cases like I described that would cause either allocator to do extra splits/joins or be slow in other ways. I expect xcfmalloc() to be slowest when it is allocating and has to break down a reserve page. Let's say it does a bunch of ~3kb allocations and has no pages on the freelists, it will: 1. scan each of the 64 freelists heads (512 bytes of cache) 2. split a 4k page 3. reinsert the 1k remainder Next time, it will: 1. scan, and find the 1k bit 2. continue scanning, eventually touching each freelist... 3. split a 4k page 4. reinsert the 2k remainder It'll end up doing a scan/split/reinsert in 3/4 of the cases, I think. The case of the freelists being quite empty will also be quite common during times the pool is expanding. I think xvmalloc() will have some of the same problems, but let's see if it does in practice. -- Dave _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
