On Aug 7, 2013, at 2:00 PM, Andre Oppermann <an...@freebsd.org> wrote:
> On 07.08.2013 09:18, Luigi Rizzo wrote: >> On Wed, Aug 7, 2013 at 5:26 AM, Mike Karels <m...@karels.net >> <mailto:m...@karels.net>> wrote: >> Jumping to (near) the end of the thread, I like most of Andre's proposal. >> Running with minimal locks at this layer is an admirable goal, and I agree >> with most of what was said. I have a few observations on the general >> changes, >> or related issues: >> >> There was mention of taskqueues. I think that with MSI-X, taskqueues >> should not be needed or used. More specifically, having separate ithreads >> and taskqueues, with ithreads deferring to taskqueues after some limit, >> makes >> sense only for MSI and legacy interrupts. With MSI-X, an interrupt thread >> should be able to process packets indefinitely with sufficient CPU >> resources, >> and there is no reason to context switch to a different thread >> periodically. >> A periodic "yield" might be reasonable, but if it is necessary, small >> packet >> performance will suffer. However, most of this is internal to the driver. >> >> >> i am not completely clear on what is the difference between ithreads and >> taskqueues. > > The difference between ithreads and taskqueues is actually very small and > mostly in > name and how they're set up and kicked off when work is to be done. Both are > real > kernel threads. Most of the confusion, also in Mikes response, seems to come > from > the name ithreads for interrupt-threads. However an ithread is not running in > interrupt context, only the interrupt handler (called filter) does. > Scheduling a > taskqueue from an ithread is a bit round-about but commonly done. The > bus_setup_intr(9) > man page isn't helping to clear up the confusion. > I think it might still be the case that threads are not allowed to sleep. That means no sx locks and no malloc(M_WAITOK), along with the obvious tsleep/msleep. Taskqueues have no such restriction. An even rore relevant difference is that taskqueues have a much stronger management API. Ithreads can only be scheduled by generating a hardware interrupt, can only be drained by calling bus_teardown_intr(), and cannot be paused. Taskqueues give you direct access to this control. Scott _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
