Scott Long writes: > > Touching the APIC is tricky. First, you have to pay the cost of a > spinlock. Then you have to may the cost of at least one read and write > across the FSB. Even though the APIC registers are memory mapped, they > are still uncached. It's not terribly expensive, but it does add up. > Bypassing this and using a fast interrupt means that you pay the cost of > 1 PCI read, which you would have to do anyways with either method, and 1 > PCI write, which will be posted at the host-pci bridge and thus only as > expensive as an FSB write. Overall, I don't think that the cost > difference is a whole lot, but when you are talking about thousands of > interrupts per second, especially if multiple interfaces are running > under load, it might be important. And the 750x and 752x chipsets are > so common that it is worthwhile to deal with them (and there are reports > that the aliasing problem is happening on more chipsets than just these > now).
I think you've sold me. I'm in the process of trying to justify time to write a FreeBSD driver for our PCIe 10GbE cards, and I find what you're doing fascinating. I'd like to use some of your techniques for the driver I'm writing. > As for latency, the taskqueue runs at the same PI_NET priority as an the > ithread would. I thought that there was an optimization on some > platforms to encourage quick preemption for ithreads when they are > scheduled, but I can't find it now. So, the taskqueue shouldn't be all > that different from an ithread, and it even means that there won't be > any sharing between instances even if the interrupt vector is shared. OK that (a taskqueue not getting the same fast preemption an ithread would) was just what I was afraid of. I'm glad that it is not a problem. <...> > However, taskqueues are really just a proof of concept for what I really > want, which is to allow drivers to register both a fast handler and an > ithread handler. For drivers doing this, the ithread would be private Ah, the darwin / MacOSX model. That would be very cool. Anyway, keep up the good work. It is inspiring! Drew _______________________________________________ cvs-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/cvs-all To unsubscribe, send any mail to "[EMAIL PROTECTED]"
