Messages in this thread | | | Date | Wed, 26 Apr 2006 19:42:35 +0200 | From | Jens Axboe <> | Subject | Re: Lockless page cache test results |
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On Wed, Apr 26 2006, Andrew Morton wrote: > Jens Axboe <axboe@suse.de> wrote: > > > > Running a splice benchmark on a 4-way IPF box, I decided to give the > > lockless page cache patches from Nick a spin. I've attached the results > > as a png, it pretty much speaks for itself. > > It does. > > What does the test do? > > In particular, does it cause the kernel to take tree_lock once per > page, or once per batch-of-pages?
Once per page, it's basically exercising the generic_file_splice_read() path. Basically X number of "clients" open the same file, and fill those pages into a pipe using splice. The output end of the pipe is then spliced to /dev/null to toss it away again. The top of the 4-client vanilla run profile looks like this:
samples % symbol name 65328 47.8972 find_get_page
Basically the machine is fully pegged, about 7% idle time.
We can speedup the lookups with find_get_pages(). The test does 64k max, so with luck we should be able to pull 16 pages in at the time. I'll try and run such a test. But boy I wish find_get_pages_contig() was there for that. I think I'd prefer adding that instead of coding that logic in splice, it can get a little tricky.
-- Jens Axboe
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