On 8/22/07, Dor Laor <[EMAIL PROTECTED]> wrote: > >> > >>> This is QEMU, with dynticks and HPET: > >> > >>> > >> > >>> % time seconds usecs/call calls errors syscall > >> > >>> ------ ----------- ----------- --------- --------- > ------------- > >--- > >> > >>> 52.10 0.002966 0 96840 > clock_gettime > >> > >>> 19.50 0.001110 0 37050 > timer_gettime > >> > >>> 10.66 0.000607 0 20086 > timer_settime > >> > >>> 10.40 0.000592 0 8985 2539 sigreturn > >> > >>> 4.94 0.000281 0 8361 2485 select > >> > >>> 2.41 0.000137 0 8362 gettimeofday > >> > >>> ------ ----------- ----------- --------- --------- > ------------- > >--- > >> > >>> 100.00 0.005693 179684 5024 total > >> > >>> > >> > >>> > >> > >> This looks like 250 Hz? > >> > >> > >> > > > >> > > Nope: > >> > > > >> > > # CONFIG_NO_HZ is not set > >> > > # CONFIG_HZ_100 is not set > >> > > # CONFIG_HZ_250 is not set > >> > > # CONFIG_HZ_300 is not set > >> > > CONFIG_HZ_1000=y > >> > > CONFIG_HZ=1000 > >> > > > >> > > and I'm reading it from /proc/config.gz on the guest. > >> > > > >> > > >> > Yeah, thought so -- so dyntick is broken at present. > >> > >> I see a lot of sub ms timer_settime(). Many of them are the result of > >> ->expire_time being less than the current qemu_get_clock(). This > >> results into 250us timer due to MIN_TIMER_REARM_US; this happens only > >> for the REALTIME timer. Other sub-ms timers are generated by the > >> VIRTUAL timer. > >> > >> This first issue is easily fixed; if expire_time < current time then > >> the timer has expired and hasn't been reprogrammed (and thus can be > >> ignored). > >> VIRTUAL just becomes more accurate with dyntics, before multiple > >> timers were batched together. > >> > >> > Or maybe your host kernel can't support such a high rate. > >> > >> I don't know... a simple printf tells me that the signal handler is > >> called about 1050 times per second, which sounds about right. > > > >...unless strace is attached. ptrace()'ing the process really screw up > >the timing with dynticks; HPET is also affected but the performance > >hit is not as severe. > > > I didn't figure out how you use both hpet and dyn-tick together.
I don't. Only one timer source is active at any time; the selection is done at startup with -clock option. > Hpet has periodic timer while dyn-tick is one shot timer each time. > Is ther a chance that both are working and that's the source of our > problems? No, the various sources are exclusive (though it might be possible to use HPET in one shot mode). Luca