On Fri, 6 Aug 2021, Daniel Wagner wrote: > Hi Alison, > > On Thu, Aug 05, 2021 at 01:16:17PM -0700, Alison Chaiken wrote: > > The advice in the RT wiki > > > > https://rt.wiki.kernel.org/index.php/HOWTO:_Build_an_RT-application#Hyper_threading Note that the above wiki is defunct, the current one to read is: https://wiki.linuxfoundation.org/realtime/start > > > > about configuring the kernel and building RT applications was written > > in 2014, when we were on the 3.x series. That makes one wonder how > > relevant some of it is for the 5.x series, especially since processors > > in common use have changed some since then. Some of the advice, > > notably about power management, obviously is timeless. > > > > In particular, Daniel Wagner added: > > > > https://rt.wiki.kernel.org/index.php/HOWTO:_Build_an_RT-application#Hyper_threading > > > > "Hyper threading and also out of order execution of CPUs introduces > > 'random' latencies. As mentioned in power management, it is > > recommended to disable these feature (if possible) or carefully > > benchmark the performance." > > > > Is the advice still current? > > I don't think the situation has changed. Though, I don't run these test > on modern hardware on regular basis. The last time I played with it on a > bit more modern hardware it was still measurable by cyclictest with > hackbench as workload. > > > Should we RT-users all still turn hyperthreading off? > > Obviously, it depends on your use case. If your application can tolerate > the added noise by SMT, you don't have to disable it. > > > Given the security vulnerabilities associated > > with hyperthreading, there are clearly some use cases where doing so > > is indicated anyway. > > Again it depends on your use case. > > Daniel > The safe answer is always to measure it. John
