Messages in this thread | | | Date | Thu, 6 Jul 2000 00:55:20 +0200 | From | Pavel Machek <> | Subject | Re: a joint letter on low latency and Linux |
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Hi!
> > On Wed, 5 Jul 2000, Richard Gooch wrote: > > > RTLinux doesn't have to be conservative this way. It doesn't have to > > > work around broken hardware ("Oh, it hangs? Go use decent hardware"). > > > This is a key point I'm finding difficult to get across. > > > > Youre saying we cant do better than 4000ms? Ouch. > > I'm saying we can't do better than N ms, where N is an unknown > quantity (because all drivers and core kernel code has not been > audited, and said auditing would take man-years and be an ongoing > project). And people have reported large values of N. Apparently the > PS/2 driver has N >= 50. There may be other stuff that is much worse. > I think Andrew Morton measured something with N = 160.
With fbcon on machine with loaded PCI bus (usb modem), N can be ~500, even more with really full screen. You know, fbcon is running with interrupts disabled.
> But people should not fool themselves into thinking that anybody has a > clue how big N could be. Even with a specific hardware combination, > there may always be some kernel slow algorithm that is lurking, ready > to blow out N.
Pavel -- I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care." Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org
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