| Date | Thu, 10 Jan 2002 19:18:23 -0800 | From | Andrew Morton <> | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable |
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Nigel Gamble wrote: > > On Thu, 10 Jan 2002, Alan Cox wrote: > > The fun below 1mS comes from > > > > 1. APM bios calls where the bios decides to take >1mS to have > > a chat with your batteries > > 2. Video cards pulling borderline legal PCI tricks to get > > better benchmarketing by stalling the entire bus > > Don't forget the embedded space, where the hardware vendor can ensure > that their hardware is well-behaved. Even on a PC, it is possible for > someone who cares about realtime to spec a reasonable system. > > On good hardware, we can easily do much better than 1ms latency with a > preemptible kernel and a spinlock cleanup. I don't think the > limitations of some PC hardware should limit our goals for Linux. >
On 700MHz x86 running Cerberus we can do 50 microseconds average and 1300 microseconds worst-case today.
Below 1000 uSec, the required changes get exponentially larger and more complex. I doubt that it's sane to try to go below a millisecond on a desktop-class machine with desktop-class workload, disk, memory and swap capacities.
On a more constrained system, which is what I expect you're referring to, 250 microseconds should be achievable. Whether or not that is achieved via preemptability is pretty irrelevant.
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