Messages in this thread | | | Date | Fri, 25 Sep 1998 18:58:22 +0100 | From | Jamie Lokier <> | Subject | Re: Interesting scheduling times - NOT |
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On Thu, Sep 24, 1998 at 11:51:40PM -0600, Larry McVoy wrote: > You have no evidence that these changes are needed, you have > a benchmark that is pretty useless for measuring these changes, and yet > you insist that the kernel gets changed. No, no, no, no. That's not > engineering, that's voodoo.
[To Larry]: The voodoo point is a good one. Richard does have results that show his changes to be effective for his program, but he hasn't shown us _why_ they are effective. Sure, fewer cache lines touched etc. but I think we all agree that doesn't explain his results.
If Richard's changes ever make their way in, without a proper understanding of the causes those changes will get lost in future reengineering anyway. There's no point putting them in now, unless it makes the code simpler.
[To Richard]: Richard, I suggest you go hunting for the real cause of your wildly varying numbers. You've found some clues (length of run queue, layout of task_struct).
You're talking about cache effects. Now those are usually rather subtle and fragile effects. It's quite possible your fix works because it changes the length of scheduler function, thereby changing the placement of various kernel code and data, or some equally fragile reason.
[ Still beats me why L1 data caches don't XOR the low address bits with a hash of the high address bits to get the line address, it would fix many of the annoying line conflict problems. ]
-- Jamie
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