Messages in this thread |  | | | From | "Davide Libenzi" <> | | Subject | Re: Interesting analysis of linux kernel threading by IBM | | Date | Fri, 21 Jan 2000 09:12:47 +0100 |
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Friday, January 21, 2000 1:53 AM Larry McVoy <lm@bitmover.com> wrote :
Hi Larry,
> : I really don't understand Your position. > : If we can have the same performance under "home" situations and be prepared to > : high load under either real world servers or benchmarks, why we don't do it ? > > Because it is this line of reasoning that makes operating systems die. > You are micro optimizing for a particular case. That's just plain BAD > in an operating system. Special cases are BAD BAD BAD. > > And I've heard a million times "it's only 1%" or "I benchmarked it and it > was the same". Of course it was only 1%, you only made one change. But > there are 100s of engineers all saying "it's only 1%".
have You seen the current schedule() implementation ? It's filled of goto to keep a linear CPU fast-path with blocks with lower probability of execution kept in tail of the function block. To gain how in percent ? My patch, IMVHO is more clear then goto jump-back solution, under normal cases gives the same results, while under I load gives much better performance.
> : Anyway I think benchmarks have their importance coz they drive servers choice > : decisions as long as stability issues. > > Look, I'm world wide famous for my benchmarking skill. I think benchmarks > are important too but only if they represent a distilled version of > an application, not a contrived situation. I can contrive a million > different situations all of which are meaningless.
Remeber that not always strategic decisions are taken by cultured ( in a computer science sense ) persons, otherwise Apple would defeat MSDOS and OS2 would defeat Windows 3.0. Anyway I prefer stability too, but if You can have both, why not ?
> : High threaded applications gives a better results given that are well designed > : with a fine resource locking system. > > Really? So what's the biggest application of that sort that you've > designed or substantially implemented? Anything as big as the kernel? > Me personally, I've worked on IRIX (scales to about 256 processors well, > and to 2048 poorly) and Solaris (scales to mebbe 64 on a good day, > usually more like 16-32). I've done in depth, multi year performance > work on both of those platforms. I was sitting next door to Steve > Kleiman when he was designing the SunOS multithreading architecture, > which heavily influenced the POSIX spec. We used to discuss this daily.
Sorry I wouldn't have bothered a guru ;) I've sure a lower experience then Your but I continue to prefer a high threaded application with fine grained locks. It'll be prepared for well scaling SMP systems, that IMVHO will be the future of computing, rather than uniprocessor ones with 1e99 gates ;)
Anyway I'd like if You get a look at the patch. I think that a logarithmic scheduler, bechmarks apart, helps Linux SMP to scale better.
Cheers, Davide.
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