Messages in this thread | | | From | Benno Senoner <> | Subject | Re: scheduling latencies, [patch] `cp /dev/zero /tmp' (patch against 2.2.9) | Date | Fri, 18 Jun 1999 00:06:47 +0200 |
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On Thu, 17 Jun 1999, Alan Cox wrote: > > The process does only sit in a loop and write() data from RAM to /dev/dsp > > ( RT FIFO scheduled), > > and in background I call scripts which write / copy / read from/to large files, > > trying to disturb the RT thread. > > Obviously my disk I/O processes are scheduled without realtime priority. > > > > The scheduling latencies on Linux go up to 70-130ms on pretty high end HW. > > What hard disk controller, if its IDE how is it tuned (DMA/UDMA, irq masked ?) > If it is a random socket7 board what fairness settings have you got in the > BIOS as by default on some of these boards IDE DMA can hog the entire bus. > > Alan
PII 400 + Mainboard Asus P2B BX Chipset, with a IBM Deskstar 16GB UDMA as /dev/hdc
tu tune the disk I enabled all useful features:
multicount , DMA , unmask IRQs , enable 32 bit support
/sbin/hdparm -m 8 -d 1 -u 1 -c /dev/hdc
note that windoze is able to get the 20ms latency with my machine , using a software synthesizer, and copying a file in the background, Maybe they use some hacks like IRQ programming, but I think with clever scheduling , you can reach similar results using RT processes.
try my benchmark yourself:
http://www.gardena.net/benno/linux/latencytest0.3.tgz
to note that heavy access to the /proc filesystem (using top -d 0.01 ) causes audio drop outs too, not so long as disk access, in the range of 15ms , but that seems a bit high for me.
we really need an *UGLY* (but useful) hack which allows the write() to soundcards, to skip some locks of the I/O layer, since audio writes are completely unrelated to disk I/O , but I have no idea how hard it would be to implement such a mechanism.
let me know if there are new advances in this area !
regards, Benno.
sbenno@gardena.net
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