On Wed, 2002-11-27 at 00:25, thomas wrote:
> Where do the -15 and +15 come from and what do they actually map to? They are windows priorities. They come from the win32 headers. We don't map to *either* of them, because Cygwin is not suitable for running programs at realtime priority and IIRC there was some iisue about running at idle too. > Also THREAD_PRIORITY_TIME_CRITICAL is not mapped in sched.cc to any UNIX > priority so if an application calls See above. > SetPriorityClass(GetCurrentProcess(), REALTIME_PRIORITY_CLASS) > SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_TIME_CRITICAL) > > what happens actually? As you already say in sched.cc: "We don't want > process's going realtime" i guess it doesn't run at -20 but some other > priority. If you do that, expect to get a hung system real fast. Windows doesn't avoid priority inversions, and the *only* programs that should run at realtime priority are those designed for it. Cygwin is a general purpose tool, and internally not quite up to running at realtime when I wrote that mapping logic. > > those tests show nothing other than the time it takes to push the iso > > through to a bitbucket. Unless there is serious other load on the CPU, > > the time *should* be constant. > > I've run the test many times and they all give the same result, > switching from nice -0 to nice --1 always gives a horrible delay, the > cpu is not doing any other work at all during the test. But this seems > to be an application specific problem and we're still investigating > this. What happens with nice -20 ? > While i was writing this i had the idea to do the same test with cat > instead of mkisofs with a quite interesting result: > > $ time cat test.iso | nice -1 dd of=/dev/null > real 0m7.171s > user 0m2.466s > sys 0m4.733s > > $ time cat test.iso | nice -0 dd of=/dev/null > real 0m7.205s > user 0m2.794s > sys 0m4.467s > > $ time cat test.iso | nice --1 dd of=/dev/null > real 1m51.428s > user 0m0.107s > sys 0m0.015s Ah, I see it now, you expect a higher priority, and get less performance. What happens if you do this: time nice --1 cat test.iso | nice --1 dd of=/dev/null ? > I've briefly looked through the pre-1.3x sources and i can't find > sched.cc there or sth. of the like, how was it handled back then? sched.cc It was introduced around 1.1 IIRC. I may be remembering wrongly :}. CVS is your friend. Rob -- --- GPG key available at: http://users.bigpond.net.au/robertc/keys.txt. ---
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