[RC5] Re: Needing testers (Mac OS X/G5)

Elektron elektron_rc5 at yahoo.ca
Mon Aug 9 16:07:35 EDT 2004


>> and though it supports nice 20, still manages to screw up scheduling 
>> (and top doesn't show the priority). When more processes are 
>> competing, it seems to do it better.
>
> It simply depends on your design goals I guess. When I reported that 
> nice level 20 did something different than only consuming idle time, 
> my bug report was closed as "behaves correctly".
>
> Mac OS X has many more priority levels than the traditional -19..20 
> (and indeed different classes of priorities), and the system is mainly 
> built for low latencies (which are still quite remarkable compared to 
> most other systems out there afaik, including Linux and FreeBSD) and 
> giving consistent/guaranteed maximum latencies under heavy load, than 
> getting optimal performance in all cases.

ps (and top) take up far too much cpu time for me to believe it's 
supposed to involve 'low latencies'. top takes up 5% of a p133 running 
some old version of redhat, but 10% of a G4/700 (and I'm not running 
that many more processes). Each process isn't even guaranteed the 10000 
microsecond timeslice of cpu time (which is easy enough to check by 
monitoring the TB), the median is 1200 on heavy load. The highest is 
only 8200. If I allow for gaps of 1% of the timeslice, the median is 
still 3400 (though the highest is 15000).

>> (OSX's memory management is horrible).
>
> It has little to do with bad memory management by the OS. If you check 
> the output from vmmap, you'll see there's 16MB malloc'ed (but 
> otherwise largely unused) memory that forms a large part of that 
> memory. There's also an 8MB stack though, which is quite large.

I know it's allocated and untouched, but that doesn't make OSX's memory 
management any less horrible. OSX's file cache is worse than windows' - 
the time I accidentally turned VM off, everything ran faster (maybe I 
should try this again). I shouldn't need to set F_NOCACHE so that 
checksumming disk images doesn't take forever because it has to page 
out, or lag everything afterwards because things have to be paged in.

Then there's other quirks, like the incorrect format strings in 
hotfiles_evict (it's probably time to defrag, but I don't know how much 
I trust Norton with HFSX).

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