Hi, On Wed, Sep 17, 2014 at 1:46 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: > Why would we need/want per process vvar contents? It seems better to > have the code swapped out. We are looking at the migration use case (CRIU). In specific, we want to make CLOCK_MONOTONIC keep the "monotonic" promise after migration. In order to accomplish that, we may need to add an offset to CLOCK_MONOTONIC calls after migration. By keeping a per process vvar page we should be able to implement that without having to fallback to a real syscall for calls to clock_gettime(CLOCK_MONOTONIC). One other thought was that we could use this process vvar page to expose a migration counter that would get incremented after migration. That way we could allow (some) userspace tasks (and possibly some VDSO routines) to use RDTSC but check the contents of that counter before/after taking measurements to check whether the elapsed time is valid or not. That means we could still provide tasks with a fast time counter if they really need one. Cheers, Filipe -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
