On Mon, Apr 29, 2019 at 07:49:24AM -0700, Paul E. McKenney wrote: > On Mon, Apr 29, 2019 at 10:19:44AM +0200, Sebastian Andrzej Siewior wrote: > > On 2019-04-26 06:50:58 [-0700], Paul E. McKenney wrote: > > > One place to look is in the summary output: > > > > > > TREE01 ------- 17540 GPs (58.4667/s) [rcu: g130629 f0x0 ] > > > > > > The "58.4667/s" is the number of grace periods per second. I would be > > > surprised if CONFIG_PARAVIRT_SPINLOCKS made a noticeable difference in > > > grace-period rate (given the natural variation), but you never know. > > > > I did four runs of the different parts of the patch: > > - 5.1-rc6 > > - #1 + kvm64 CPU + some config options > > - #2 + tsc-deadline=on and so on (the whole line) > > - #3 + CONFIG_PARAVIRT_SPINLOCKS (now everything) > > > > the test command was > > tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 112 --duration 60 --configs "16*TREE08" --memory 4G > > > > and the results: > > | HEAD is now at 085b7755808a... Linux 5.1-rc6 > > | (28.5942 +27.4658 +28.0203 +27.2061 +28.0731 +26.9078 +27.8494 + 27.3392 +26.4339 +28.025 +27.4797 +27.6775 +28.0653 +28.0742 +27.9581 +28.6508)/ 16 > > | 27.738775 > > | > > | HEAD is now at 36a12aa9761a... tune #1 > > | (28.5761 +26.6514 +26.6989 +27.4375 +27.3442 +28.3228 +26.6353 +27.5461+28.5531 +27.7006 +27.8078 +27.9753 +27.4269 +28.0464 +27.6314 +27.8356) / 16 > > | 27.6368375 > > | > > | HEAD is now at af5cd7196436... tune #2 > > | (28.4867 +26.3675 +27.6364 +28.3344 +27.4153 +27.9306 +27.1703 +26.8461+27.3194 +28.5486 +27.8975 +27.4356 +28.12 +28.4397 +29.0186 +26.9328 )/ 16 > > | 27.74371875 > > | > > | HEAD is now at 3701f64943f5... tune #3 > > | (28.2431 +27.7831 +28.39 +28.2586 +27.7408 +27.9258 +26.6236 +26.7817+29.1178 +26.9564 +29.0525 +27.4258 +27.4931 +27.8928 +26.9308 +28.4833)/ 16 > > | 27.8187 > > > > This 28.… is the number of GP/s. Based on the results in looks like > > noise to me. Also I have no idea why you have more than twice as many > > GP/s as I do. > > My guess is that because you have more CPUs, the for_each_online_cpu() > loop takes longer on your system. OK, that is rather oversimplified, to say the least. A better way to put this is that the probability of some CPU holding things up is larger the more CPUs you have. RCU doe take explicit steps to slow down grace periods, but that doesn't start kicking in until 256 CPUs. Thanx, Paul > > Different box doing: > > tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 112 --duration 60 --configs "42*TREE01" --memory 4G > > and got this: > > > > | HEAD is now at 085b7755808aa... Linux 5.1-rc6 > > | (15.2878 + 15.8664 + 15.6369 + 15.6714 + 15.3667 + 16.4706 + 15.7844 + > > | 16.2119 + 15.6108 + 15.84 + 16.0003 + 16.2886 + 15.8728 + 15.5347 + > > | 15.6753 + 15.6628 + 15.8628 + 15.8158 + 15.8419 + 16.0053 + 15.7878 + > > | 16.465 + 16.2267 + 16.6881 + 16.3186 + 16.1778 + 15.7069 + 16.0178 + > > | 15.7156 + 16.0083 + 15.7181 + 15.8961 + 15.5253 + 16.1569 + 15.7692 + > > | 16.2622 + 16.2931 + 15.9531 + 15.6697 + 15.4539 + 15.6478 + 15.8047) / > > | 42 > > | ~15.89452142857142857143 > > | > > | HEAD is now at 3701f64943f5a... tune #3 > > | ; (15.8461 + 15.8653 + 16.0392 + 15.8906 + 15.7606 + 15.6169 + 16.1425 + > > | 15.9089 + 16.2169 + 16.1694 + 16.2122 + 15.6417 + 15.8022 + 16.1178 + > > | 15.1689 + 16.1303 + 16.0181 + 16.3797 + 16.0614 + 16.2839 + 15.4583 + > > | 15.9178 + 16.0589 + 16.3428 + 15.5486 + 16.0839 + 15.9931 + 15.8417 + > > | 16.0981 + 15.8075 + 15.9925 + 15.7311 + 15.9172 + 16.1164 + 15.6303 + > > | 15.9383 + 16.0714 + 16.2786 + 15.8394 + 15.9597 + 16.0175 + 15.3908) / > > | 42 > > | ~15.93586904761904761905 > > > > Noise. > > > > So from RCUtorture point of view there is no improvement right? In that > > case I would suggest to drop the problematic parts… > > Thank you for testing this! I will adjust accordingly. > > Thanx, Paul
