On 05/01/2015 12:45 PM, Ingo Molnar wrote: > > * Rik van Riel <[email protected]> wrote: > >> On 05/01/2015 12:37 PM, Ingo Molnar wrote: >> >>> Also note that this bit in context_tracking_enter(): >>> >>> if (state == CONTEXT_USER) { >>> trace_user_enter(0); >>> vtime_user_enter(current); >>> } >>> >>> >>> is related to precise time measurement of user/kernel execution >>> times, it's not needed by the scheduler at all, it's just exported >>> to tooling. It's not fundamental to the scheduler. >> >> Any objections to the idea from the other thread to simply keep the >> time accumulating in buffers in local_clock() units, and only update >> the task vtime once a second or so? > > So I really think per syscall overhead is the wrong thing to do for > anything that a common distro enables. > > I see very little use for such precise, high-freq measurements on > normal systems - and abnormal systems could enable it dynamically just > like they can enable syscall auditing. > > I.e. I don't mind the occasional crazy piece of code, as long as it > does not hurt the innocent.
Then how should/could we keep a rough idea of user / system / guest time when running without a periodic timer tick? These statistics are useful, and gathering them in a low impact way (local_clock read + variable read + subtraction + addition + store) may be acceptable overhead. This is a few function calls, one tsc read, a possible cache line miss, and an unlikely branch. -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
