On 05/01/2015 01:12 PM, Ingo Molnar wrote: > > * Rik van Riel <[email protected]> wrote: > >> 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? > > So I'd split the timer tick into two parts: just the constant-work > sampling bit that doesn't do much, and the variable-work part which > gets essentially shut off when the timeout is far into the future. > > Then we could do IRQ driven sampling without introducing variable > amount jitter into hard-RT execution time. > > I.e. much of what we do today, except that we could skip variable work > such as the scheduler tick or (unforced) RCU processing like the RCU > softirq work.
Any ideas how we could avoid that sampling timer interrupt latency stacking up when dealing with both guest and host? -- 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/
