Messages in this thread | | | Date | Sun, 29 Aug 1999 11:09:09 -0700 | From | Brian Swetland <> | Subject | Re: [alsa-devel] Re: [rtl] Low-latency patches working GREAT (<2.9ms audio latency), see testresults ,but ISDN troubles |
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[yodaiken@chelm.cs.nmt.edu] > On Sun, Aug 29, 1999 at 10:40:02AM -0700, Brian Swetland wrote: > > [yodaiken@chelm.cs.nmt.edu] > > Well, as you point out, BeOS is not a hard realtime system, however > > the fact that the filesystem, block cache, drivers, etc are all > > preemptable means you can get some pretty decent response. Interrupt > > response from timers or IO interrupts in the 30-60us range is certainly > > doable. It'd be neat to actually put together some benchmarks to > > compare this sort of thing. > > It would be quite interesting. My prediction is that the fully premptable > nature of the system makes high bandwidth i/o unlikely. I'd really like > some data though.
Well, if you have a bunch of realtime / high priority threads running, they quite possibly can cut into your IO performance. If you're doing large reads/writes that bypass the cache (>64KB or on request via ioctl) the driver (provided the device is fairly modern) should be able to do dma into/outof userspace which can be a nice win.
I'm actually working on rewriting an old interrupt latency benchmark (predating the programmable timers in R4.x) to see if I can get some real numbers here. Technically interrupts should be fieldable in the 5-10us range provided there's not a misbehaving driver disabling IRQs for extended periods of time.
> > Networking on BeOS is not stellar, but it's servicable and performance > > issues are being worked on. Raw disk IO is actually pretty good, to my > > knowledge, though obviously real numbers are what you want here and > > Raw disk and FS performance are really different. DOS gets decent raw > disk performance, but our experience is that app ports to RTLinux get > an enormous benefit from ext2.
I believe Dominic found that BFS tends to see about 5% worse performance for raw streaming IO than reading/writing the raw device. File creation/ deletion/etc suffers some due to journaling and indices (though indices can be turned off). Not much seems to beat ext2 for pure speed.
Brian
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