On 19-Oct-2006 Scott Long wrote: > The performance measurements that Andre and I did early this year showed > that the INTR_FAST handler provided a very large benefit.
I'm trying to understand why that's the case. Is it because an INTR_FAST interrupt doesn't have to be masked and unmasked in the APIC? I can't see any other reason for much of a performance difference in that driver. With or without INTR_FAST, you've got the bulk of the work being done in a background thread -- either the ithread or the taskqueue thread. It's not clear to me that it's any cheaper to run a task than it is to run an ithread. A difference might show up if you had two or more em devices sharing the same IRQ. Then they'd share one ithread, but would each get their own taskqueue thread. But sharing an IRQ among multiple gigabit NICs would be avoided by anyone who cared about performance, so it's not a very interesting case. Besides, when you first committed this stuff, INTR_FAST interrupts were not sharable. Another change you made in the same commit (if_em.c revision 1.98) greatly reduced the number of PCI writes made to the RX ring consumer pointer register. That would yield a significant performance improvement. Did you see gains from INTR_FAST even without this independent change? John _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "[EMAIL PROTECTED]"
