Messages in this thread | | | Date | Thu, 8 Apr 1999 13:22:25 -0400 (EDT) | From | Chuck Lever <> | Subject | Re: [PFC]: hash instrumentation |
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On Thu, 8 Apr 1999, Andrea Arcangeli wrote: > In the meantime only if you have some spare time, could you do a bench > over my last 2.2.5_arca8.bz2? It has major changes in the buffer code > (fixed flushtime and fixed the way buffers are flushed to disk by > bdflush). It works as never before here also under swapping (performances > visible with eyes ;).
i haven't tried all of arca8 yet, but i did sniff around in the bdflush logic to see what you tried out. i took a stock 2.2.5 kernel and took out the "run_task_queue()" in wakeup_bdflush() just to see what that it would do. that made things a little worse, so i'm guessing you also had some compensatory changes in other areas.
i'm interested to see how your flushtime changes will effect performance.
> in arca8 I restored the o+offset in the hash function, feel free to remove > it before running the bench if you think it will harm (the +offset is not > needed until you'll be very low on memory and it looks like to me that > your machine never gets low on memory ;).
i'm discovering that a 13 bit hash mitigates the spikey size distribution in the page hash *better* than the +offset change. although i've been able to push the system into swap, i still haven't seen any degenerate hash behavior that's as bad as the buffer cache's hash function.
i'll have more as i test this further.
> Ah and also the first pagemap-cachealigned patch was wrong (blame me). The > second patch (after Eric pointed out to think about it twice) does the > right thing (so you may consider to run the bench on it again... excuse > me). So probably this is the reason that the pagemap-aligned+irq-aligned > bench was weird...
i suspected that the strange performance behavior wasn't an implementation problem, so i tried a plain 2.2.5 kernel with just the page struct alignment mod in your latest patch. the numbers were about the same as before. it would probably be a good idea if someone could actually take a close look at what the alignment mod is doing to change hardware behavior, 'cause it's obviously not what we expect.
- Chuck Lever -- corporate: <chuckl@netscape.com> personal: <chucklever@netscape.net> or <cel@monkey.org>
The Linux Scalability project: http://www.citi.umich.edu/projects/citi-netscape/
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