On Wed, 16 Oct 2013, Andrew Morton wrote: > > usermodehelper() threads can currently run on all processors. > > This is an issue for low latency cores. > > How much of an issue? The severity of the problem is utterly unclear > from this description.
This causes a context switch and processing to occur. Can take up to microseconds which is a pretty long timeframe when decisions have to be made in microseconds by active processing. This will cause a trade to fail. > > - /* We can run anywhere, unlike our parent keventd(). */ > > - set_cpus_allowed_ptr(current, cpu_all_mask); > > + /* We can run anywhere kthreadd can run */ > > This is a poor comment - it explains "what" (which was utterly obvious) > but doesn't explain "why". The reader will want to know *why* > call_usermodehelper() only runs on kthreadd CPUs, but we didn't tell > him. We'd like to have the ability to avoid running usermodehelper on certain cpus to avoid cpu holdoff situations? Would that we an acceptable explanation? Or restricting kthreadd will also restrict usermodehelper spawning to allow control for all spawned kernel threads? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
