On Tue, Nov 09, 2021 at 10:29:25PM -0800, Stephen Hemminger wrote: > On Wed, 10 Nov 2021 04:20:52 +0000 > Tyler Retzlaff <roret...@microsoft.com> wrote: > > > > > > > > > High performance applications benefit from an option to raise the > > > > priority of their threads to avoid being preemted by other threads on > > > > the system. If there are issues with realtime priority on some of the > > > > platforms, maybe we can add a warning for the user to make them aware > > > > of possible crashes as Stephen H. suggested some time ago. Note that > > > > this patch doesn't change the priority of EAL threads, enabling the > > > > higher priority will be done through a command line option when > > > > starting the application. > > > > Maybe we can explore raising the priority but not to the realtime > > > > level. > > > > > Let me put it more succulently. > > > Almost all DPDK applications have threads that are a 100% CPU doing > > > polling. > > > Putting those thread as real-time thread breaks Linux badly because the > > > kernel can and will try and run work on those CPU's and the system is > > > broken/unstable/dead at that point. > > > > The suggestion is that when running on Windows it should be possible for > > the application to be configured to use real-time threads, there is no > > implication that it will force real-time priority on Linux. If it doesn't > > make sense for it to be configured on Linux then don't configure it. But > > saying it shall not be configurable for any platform just because one > > platform can't make use of the configuration and those platforms have to > > run compromised makes little sense. Linux administrators are (or should > > be) knowledgeable enough to know what configuration to use. > > > > Why not just make it always return an error when real-time is requested on > Linux from a DPDK thread. > I would tend to agree with this suggestion, that we just return ENOTSUP error code for Linux. It's too easy to lock up a linux system with realtime DPDK threads. If a user really knows what they are doing and they need realtime priority on linux, they can use the linux scheduler APIs directly. However, I am ok with having such a function supported on Windows if it's needed. Unfortunately, I don't know for sure about BSD, but it probably should follow the linux approach initially unless proved safe.
/Bruce
