On 8/22/07, Luca <[EMAIL PROTECTED]> wrote: > On 8/22/07, Avi Kivity <[EMAIL PROTECTED]> wrote: > > Luca 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. Luca