On Fri, May 21, 2021 at 12:32 PM Andy Lutomirski <luto@xxxxxxxxxx> wrote: > > On Thu, May 20, 2021 at 11:36 AM Peter Oskolkov <posk@xxxxxxxxxx> wrote: > > > > Implement version 1 of core UMCG API (wait/wake/swap). > > > > As has been outlined in > > https://lore.kernel.org/lkml/20200722234538.166697-1-posk@xxxxxxx/, > > efficient and synchronous on-CPU context switching is key > > to enabling two broad use cases: in-process M:N userspace scheduling > > and fast X-process RPCs for security wrappers. > > > > High-level design considerations/approaches used: > > - wait & wake can race with each other; > > - offload as much work as possible to libumcg in tools/lib/umcg, > > specifically: > > - most state changes, e.g. RUNNABLE <=> RUNNING, are done in > > the userspace (libumcg); > > - retries are offloaded to the userspace. > > Do you have some perf numbers as to how long a UMCG context switch > takes compared to a normal one? I'm not sure what is a "normal context switch" in this context. Futex wakeup on a remote idle CPU takes 5-10usec; an on-CPU UMCG context switch takes less than 1usec; futex wake + futex wait on the same CPU (taskset ***) takes about 1-1.5usec in my benchmarks. > > --Andy
