On Sun, 1 Apr 2018, Alan Cox wrote: > > Restartable sequences are atomic with respect to preemption > > (making it atomic with respect to other threads running on the > > same CPU), as well as signal delivery (user-space execution > > contexts nested over the same thread). > > CPU generally means 'big lump with legs on it'. You are not atomic to the > same CPU, because that CPU may have 30+ cores with 8 threads per core. > > It could do with some better terminology (hardware thread, CPU context ?)
Well we call it a "CPU" in the scheduler context I think. We could use better terminology throughout the kernel tools and source. Hardware Execution Context? > > In a typical usage scenario, the thread registering the rseq > > structure will be performing loads and stores from/to that > > structure. It is however also allowed to read that structure > > from other threads. The rseq field updates performed by the > > kernel provide relaxed atomicity semantics, which guarantee > > that other threads performing relaxed atomic reads of the cpu > > number cache will always observe a consistent value. > > So what happens to your API if the kernel atomics get improved ? You are > effectively exporting rseq behaviour from private to public. There is already a pretty complex coherency model guiding kernel atomics. Improvements/changes to that are difficult and the effect will ripple throughout the kernel. So I would suggest that these areas of the kernel are pretty "petrified" (or written in stone).
