Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH v1 01/25] net: core: device_rename: Use rwsem instead of a seqcount | Date | Wed, 20 May 2020 21:37:11 +0200 |
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David Miller <davem@davemloft.net> writes: > From: Thomas Gleixner <tglx@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
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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
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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
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