On Thu, Feb 04, 2021 at 01:47:38PM -0500, Nitesh Narayan Lal wrote: > > On 2/4/21 1:15 PM, Marcelo Tosatti wrote: > > On Thu, Jan 28, 2021 at 09:01:37PM +0100, Thomas Gleixner wrote: > >> On Thu, Jan 28 2021 at 13:59, Marcelo Tosatti wrote: > >>>> The whole pile wants to be reverted. It's simply broken in several ways. > >>> I was asking for your comments on interaction with CPU hotplug :-) > >> Which I answered in an seperate mail :) > >> > >>> So housekeeping_cpumask has multiple meanings. In this case: > >> ... > >> > >>> So as long as the meaning of the flags are respected, seems > >>> alright. > >> Yes. Stuff like the managed interrupts preference for housekeeping CPUs > >> when a affinity mask spawns housekeeping and isolated is perfectly > >> fine. It's well thought out and has no limitations. > >> > >>> Nitesh, is there anything preventing this from being fixed > >>> in userspace ? (as Thomas suggested previously). > >> Everything with is not managed can be steered by user space. > > Yes, but it seems to be racy (that is, there is a window where the > > interrupt can be delivered to an isolated CPU). > > > > ethtool -> > > xgbe_set_channels -> > > xgbe_full_restart_dev -> > > xgbe_alloc_memory -> > > xgbe_alloc_channels -> > > cpumask_local_spread > > > > Also ifconfig eth0 down / ifconfig eth0 up leads > > to cpumask_spread_local. > > There's always that possibility. Then there is a window where isolation can be broken. > We have to ensure that we move the IRQs by a tuned daemon or some other > userspace script every time there is a net-dev change (eg. device comes up, > creates VFs, etc). Again, race window open can result in interrupt to isolated CPU. > > How about adding a new flag for isolcpus instead? > > > > Do you mean a flag based on which we can switch the affinity mask to > housekeeping for all the devices at the time of IRQ distribution? Yes a new flag for isolcpus. HK_FLAG_IRQ_SPREAD or some better name.
