On 25 July 2012 08:14, Luigi Rizzo <ri...@iet.unipi.it> wrote: >> I suggest doing some digging to understand why. I bet we all know the >> answer, but it would be nice to have it documented and investigated. I >> bet em(4) isn't the only device that would benefit from this? > > I am not so sure i know the answer on bare iron (and my take is that the > difference is more or less irrelevant there), but in the virtualized case > the improvement is almost surely because the code used in FAST_INTR > has a couple of MMIO accesses to disable/enable interrupts on the > card while the taskqueue runs. These are expensive in a VM > (such accesses cost ~10K cycles each, even with hw support)
Hm, really? Doing these register accesses to a virtualised em NIC in a VM is that expensive, or is there something else going on I don't understand? Adrian _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
