On 03/14/2007 02:18 PM, Jeremy Fitzhardinge wrote: > Dan Hecht wrote: >> On 03/14/2007 01:31 PM, Jeremy Fitzhardinge wrote: >>> Dan Hecht wrote: >>>> Sounds good. I don't see this in your patchset you sent yesterday >>>> though; did you add it after sending out those patches? >>> Yes. >>> >>>> if so, could you forward the new patch? does it explicitly prevent >>>> stolen time from getting accounted as user/system time or does it >>>> just rely on NO_HZ mode sort of happening to work that way (since the >>>> one shot timer is skipped ahead for missed ticks)? >>> Hm, not sure. It doesn't care how often it gets called; it just >>> accumulates results up to that point, but I'm not sure if the time would >>> get double accounted. Perhaps it doesn't matter when using >>> xen_sched_clock(). >>> >> I think you might be double counting time in some cases. >> sched_clock() isn't really relevant to stolen time accounting (i.e. >> cpustat->steal). >> >> I think what you want is to make sure that the sum of the cputime >> passed to all of: >> >> account_user_time >> account_system_time >> account_steal_time >> >> adds up to the total amount of time that has passed. I think it is >> sort of working for you (i.e. doesn't always double count stolen >> ticks) since in NO_HZ mode, update_process_time (which calls >> account_user_time & account_system_time) happens to be skipped during >> periods of stolen time due to the hrtimer_forward()'ing of the one >> shot expiry. > > OK, this will need a closer look. > > BTW, what are the properties of the vmi read_available_cycles()? Is > that a per-cpu timer? If its used as the timebase for sched_clock, how > does recalc_task_prio not get a -ve sleep time? > Available time is defined to be (real_time - stolen_time). i.e. time in which the vcpu is either running or not ready to run [because it is halted, and nothing is pending]). So, yes, it is per-vcpu. But, the sched_clock() samples are rebased when processes are migrated between runqueues; search sched.c for most_recent_timestamp. It's not perfect since most_recent_timestamp between cpu0 and cpu1 do not correspond to the exact same instant, but does prevent negative sleep time and is fairly close. Dan _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxx https://lists.osdl.org/mailman/listinfo/virtualization
