On Mon, 2007-06-25 at 15:11 -0400, Steven Rostedt wrote: > On Mon, 2007-06-25 at 14:48 -0400, Kristian Høgsberg wrote: > ... > > However, I don't really understand how you can discuss a wholesale > > replacing of tasklets with workqueues, given the very different > > execution sematics of the two mechanisms. I would think that others > > have used tasklets for similar purposes as I have and moving that to > > workqueues just has to break a bunch of stuff. I don't know the various > > places tasklets are used as well as other people in this thread, but I > > think deprecating them and moving code to either softirqs or workqueues > > on a case by case basis is a better approach. That way we also avoid > > the gross wrappers. > > The gross wrappers were a perfect way to shed light on something that is > overused, and should most likely be replaced. > > Does your system need to have these functions that are in tasklets need > to be non-reentrant? I wonder how many "irq critical" functions used > tasklets just because adding a softirq requires too much (no generic > softirq code). A tasklet is constrained to run on one CPU at a time, > and it is not guaranteed to run on the CPU it was scheduled on.
When I started the firewire work, I wasn't aware that tasklets were going away, but I knew that doing too much work in the interrupt handler was frowned upon, for good reasons. So I was looking at softirqs vs taslkets, and since using softirqs means you have to go add yourself to the big bitmask, I opted for tasklets. The comment in interrupt.h directly recommends this. As it stands, the firewire stack does actaully rely on the non-reentrancy of tasklets, but that's not a deal-breaker, I can add the necessary locking. > Perhaps it's time to add a new functionality while removing tasklets. > Things that are ok to bounce around CPUs (like tasklets do) can most > likely be replaced by a work queue. But these highly critical tasks > probably would benefit from being a softirq. > > Maybe we should be looking at something like GENERIC_SOFTIRQ to run > functions that a driver could add. But they would run only on the CPU > that scheduled them, and do not guarantee non-reentrant as tasklets do > today. Sounds like this will fill the gap. Of course, this won't reduce the number of delayed-execution mechanisms available... Kristian - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
