On Wed, 20 May 2020 21:37:11 +0200 Thomas Gleixner <t...@linutronix.de> wrote:
> David Miller <da...@davemloft.net> writes: > > From: Thomas Gleixner <t...@linutronix.de> > > Date: Wed, 20 May 2020 01:42:30 +0200 > >>> Please try, it isn't that hard.. > >>> > >>> # time for ((i=0;i<1000;i++)); do ip li add dev dummy$i type dummy; done > >>> > >>> real 0m17.002s > >>> user 0m1.064s > >>> sys 0m0.375s > >> > >> And that solves the incorrectness of the current code in which way? > > > > You mentioned that there wasn't a test case, he gave you one to try. > > If it makes you happy to compare incorrrect code with correct code, here > you go: > > 5 runs of 1000 device add, 1000 device rename and 1000 device del > > CONFIG_PREEMPT_NONE=y > > Base rwsem > add 0:05.01 0:05.28 > 0:05.93 0:06.11 > 0:06.52 0:06.26 > 0:06.06 0:05.74 > 0:05.71 0:06.07 > > rename 0:32.57 0:33.04 > 0:32.91 0:32.45 > 0:32.72 0:32.53 > 0:39.65 0:34.18 > 0:34.52 0:32.50 > > delete 3:48.65 3:48.91 > 3:49.66 3:49.13 > 3:45.29 3:48.26 > 3:47.56 3:46.60 > 3:50.01 3:48.06 > > ------------------------- > > CONFIG_PREEMPT_VOLUNTARY=y > > Base rwsem > add 0:06.80 0:06.42 > 0:04.77 0:05.03 > 0:05.74 0:04.62 > 0:05.87 0:04.34 > 0:04.20 0:04.12 > > rename 0:33.33 0:42.02 > 0:42.36 0:32.55 > 0:39.58 0:31.60 > 0:33.69 0:35.08 > 0:34.24 0:33.97 > > delete 3:47.82 3:44.00 > 3:47.42 3:51.00 > 3:48.52 3:48.88 > 3:48.50 3:48.09 > 3:50.03 3:46.56 > > ------------------------- > > CONFIG_PREEMPT=y > > Base rwsem > > add 0:07.89 0:07.72 > 0:07.25 0:06.72 > 0:07.42 0:06.51 > 0:06.92 0:06.38 > 0:06.20 0:06.72 > > rename 0:41.77 0:32.39 > 0:44.29 0:33.29 > 0:36.19 0:34.86 > 0:33.19 0:35.06 > 0:37.00 0:34.78 > > delete 2:36.96 2:39.97 > 2:37.80 2:42.19 > 2:44.66 2:48.40 > 2:39.75 2:41.02 > 2:40.77 2:38.36 > > The runtime variation is rather large and when running the same in a VM > I got complete random numbers for both base and rwsem. The most amazing > was delete where the time varies from 30s to 6m20s. > > Btw, Sebastian noticed that rename spams dmesg: > > netdev_info(dev, "renamed from %s\n", oldname); > > which eats about 50% of the Rename run time. > > Base netdev_info() removed > > Rename 0:34.84 0:17.48 > > That number at least makes tons of sense > > Thanks, > > tglx Looks good thanks for following through.
