Messages in this thread | | | Date | Sun, 12 Mar 2000 15:38:18 -0700 | From | yodaiken@fsmlabs ... | Subject | Re: new IRQ scalability changes in 2.3.48 |
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On Sun, Mar 12, 2000 at 09:53:29AM -0800, Linus Torvalds wrote: > Doing an __sti in interrupts will let higher-priority interrupts in. As it > always has.
Previously, _any_ interrupt was let to progress. That is, hardware priorities were ignored by Linux.
> I think it's probably stupid most of the time, and shows that something is > wrong (an interrupt should not take long enough for it to matter that we > do an __sti), but sometimes that kind of stupidity is a result of horrible > hardware latencies (eg the time it takes to read a sector from the IDE > disk using programmed IO).
So if we have a hardware determined higher priority level IDE than level network, then it previously was the case that if the IDE driver was polite and did an __sti, the network was assured of a relatively low latency. However, the network now may need to wait until the programmed i/o completes. Probably programmed i/o should rather happen in soft_interrupt space, but with the current drivers it does not.
> Quite regardless of how you do interrupts: it doesn't matter where youput > the ACK's, you always need to make sure that irq masking etc is correct, > and you must NOT allow a context switch while an interrupt handler is > still running.
Ok. Ingo: does your "low latency" patch violate this rule?
> You're making these problems up.
Yes. I thought that the hardware worked like 8259s, but it is somewhat more sensible.
> > I really dislike hardware interrupt priorities since they have nothing > > to do with the OS' ideas of importance and are complex to work with. > > I agree. I think interrupt controllers should be simple masks, nothing > more, nothing less. > > However, I'm not designing the hardware.
It's amazing how stubbornly hardware folks refuse to consider OS in their designs.
--------------------------------------------------------- Victor Yodaiken FSMLabs: www.fsmlabs.com www.rtlinux.com FSMLabs is a servicemark and a service of VJY Associates L.L.C, New Mexico.
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