On Fri, 16 Feb 2018, Sebastian Andrzej Siewior wrote: > On 2018-02-16 13:29:01 [-0500], Alan Stern wrote: > > We originally used tasklets because we didn't want to incur the delays > > associated with running in a process context. It seems odd to be > > reversing that decision now. > > The theaded interrupt runs SCHED_FIFO priority 50 by default. The only > thing that can interrupt it are interrupts, a softirq (not ksoftirqd) > and other tasks with a higher priority than 50. > There should be no downside performance wise. Maybe. It would be nice to see some real measurements. > > > The URBs from the root-hub never create an interrupt so I currently > > > process them in a workqueue (I'm not sure if an URB-enqueue in the > > > completion handler would break something). > > > > It worked okay before we changed over to using tasklets. > > Ah okay. I've seen that HCDs were no longer dropping their internal lock > and I wasn't sure if such a change was also applied in RH-code. Oh... my memory was faulty. After going back and looking at the old source, I see that before we switched to tasklets the code _did_ drop the hcd_root_hub_lock when giving back root-hub URBs. Now it doesn't. (It's also worth noticing that the current code gives back root-hub URBs in a tasklet even for HCDs that don't support using tasklets for non-root-hub URBs.) In any case, latency doesn't matter much for root-hub URBs. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
