On Fri, 1 Apr 2005, kus Kusche Klaus wrote: > > The biggest advantage would come from using a bottom-half > > handler to do > > most of the work. Right now the uhci-hcd driver does > > everything in its > > interrupt handler. This would certainly help IRQ latency; it > > might not > > affect application latency very much. > > Sounds very reasonable, thanks. Also helps application latency, > because with the RT patches, I can tune the rt prio of softirq > execution (that's where bottom-half goes, doesn't it?) w.r.t. the > rt prio of the application threads.
Yes. Bear in mind, however, that if these application threads are doing I/O over USB then they will be forced to wait for the bottom half to execute, regardless of its priority. > However, if I understand things correctly, if you really need > to disable all interrupts while doing the USB work, it will not > make any difference if IRQs are disabled while you are in the > USB IRQ handler, or if they are disabled for the same amount of > work/time in the bottom-half code. For most of the USB work it will be necessary only to insure that no more than one copy of the bottom-half handler is running at a time, which I think the kernel does automatically for tasklets. There are a few places where all IRQs will have to be disabled, but those places are relatively small and short. Right now, of course, everything runs with IRQs disabled. > > We'll see what happens with the upcoming changes. Maybe > > you'll be able to > > test them for me? > > Basically, yes (as long as our company doesn't decide to stop the > linux experiments). > > However, I depend on Ingo's RT patch, which is against the -rc series, > not against the -mm series. So I will probably not be able to apply > patches created against -mm. Okay. It will be a while before the new code is ready and the changes on which it depends have gotten into -rc. Alan Stern ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-users
