On 02/29/2016 11:14 AM, Thomas Gleixner wrote: > On Mon, 29 Feb 2016, Peter Hurley wrote: >> On 02/29/2016 10:24 AM, Eric Dumazet wrote: >>>> Just to be clear >>>> >>>> if (time_before(jiffies, end) && !need_resched() && >>>> --max_restart) >>>> goto restart; >>>> >>>> aborts softirq *even if 0ns have elapsed*, if NET_RX has woken a process. >>> >>> Sure, now remove the 1st and 2nd condition. >> >> Well just removing the 2nd condition has everything working fine, >> because that fixes the priority inversion. > > No. It does not fix anything. It hides the shortcomings of the driver. > >> However, when system resources are _not_ contended, it makes no >> sense to be forced to revert to ksoftirqd resolution, which is strictly >> intended as fallback. > > No. You claim it is simply because your driver does not handle that situation > properly. > >> Or flipping your argument on its head, why not just _always_ execute >> softirq in ksoftirqd? > > Which is what that change effectivley does. And that makes a lot of sense, > because you get the softirq load under scheduler control and do not let the > softirq run as a context stealing entity which is completely uncontrollable by > the scheduler. Ok, fair enough. However, charging [in the scheduler sense] very lightweight DMA completion for one subsystem collectively with very heavyweight NET_RX (doing garbage collection in softirq!) is hardly ideal. The alternative being threaded interrupt handlers (which are essentially treated as 0.000000 scheduler cost). I just want to make sure that's the conscious choice being made, when the patches for converting from tasklet to threaded irq start hitting subsystem maintainers. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
