On Mon, Sep 14, 2020 at 12:27:35PM +0100, Qais Yousef wrote: > What does PREEMPT_RT do to deal with softirqs delays?
Makes the lot preemptible, you found the patch below. > I have tried playing with enabling threadirqs, which AFAIU should make > softirqs > preemptible, right? Not yet,.. > I realize this patch is still missing from mainline at least: > > > https://gitlab.com/kalilinux/packages/linux/blob/a17bad0db9da44cd73f594794a58cc5646393b13/debian/patches-rt/softirq-Add-preemptible-softirq.patch > > Would this be a heavy handed approach to make available for non PREEMPT_RT > kernels? Not sure, I suspect it relies on migrate_disable(), which is preempt_disable() on !RT and then we're back to square one. > I only worry about potential NET_RX throughput issues. Which by the way is > protected with preempt_disable currently in mainline. See netif_rx_ni(). So preempt_disable() isn't necessairily a problem, you just want it to terminate soonish after need_resched() becomes true. Also, I'm having a wee problem getting from net_rx_action() to netif_rx_ni() > I am guessing here, but I suspect this NET_RX softirq is one source of big > delays when network activity is high. Well, one approach is to more agressively limit how long softirq processing can run. Current measures are very soft in that regard.
