Re: [PATCH 0/3] timekeeping: Improved NOHZ frequency steering (v2)

From: Miroslav Lichvar
Date: Wed Jul 16 2014 - 07:57:56 EST

On Tue, Jul 15, 2014 at 09:02:38PM -0700, John Stultz wrote:
> On 07/08/2014 04:08 AM, Miroslav Lichvar wrote:
> > It seems it may be a while before the old vsyscalls are fixed. How
> > about including only the first two patches from this set for now?
>
> Hey! Sorry for the slow response here, I was on the road the last two weeks.
>
> So thanks for the ping here. If you're happy with the first two as an
> initial step, I'd be willing to try to push those in.

Ok, thanks.

> Thomas: Would you be ok if I push you some patches to improve ntp/ptp
> freq steering w/ NOHZ for this merge window as well? So far the patches
> have only shown nice improvements and no regressions, but its clearly
> subtle code, and there's a lot going on in this merge window.

For the record, here are test results from the simulator. There is a
regression in the performance with disabled nohz, it takes longer for
the clock to converge, but I think it's acceptable. When compared on
the same time scale, disabled nohz still seems to be significantly
better than nohz enabled.

3.16-rc5:
$ ./test1.sh
freq10 freq100 dev max
nohz on 38.38368 2.72579 1468940.9 9846788.2
nohz off 3.89181 0.10436 0.2 0.6

3.16-rc5 + two patches from this set:
$ ./test1.sh
freq10 freq100 dev max
nohz on 1.13791 0.05155 85.0 313.7
nohz off 1.02364 0.05149 0.5 1.7

Here are results from a new script I added to linux-tktest, which
I think shows better how the clock is converging.

3.16-rc5:

$ ./test2.sh
nohz on [1, samples/2] [samples/2 + 1, samples]
samples freq dev max freq dev max
10 32.08360 16039.4 23435.5 39.61782 11077.4 30938.0
30 13.84304 35033.8 80321.5 8.52682 21495.6 52639.6
100 0.68945 31395.7 86405.6 1.26818 26426.9 98448.1
300 0.18118 33906.1 104062.0 0.11419 21147.4 102418.1
1000 0.02699 32254.1 120619.4 0.02234 21222.3 120107.6
3000 0.00515 31210.4 131688.9 0.00525 23067.8 140999.4
10000 0.00077 31904.1 149537.0 0.00079 21688.2 144957.5
30000 0.00015 31422.9 158176.5 0.00015 21867.9 159288.5
100000 0.00003 31301.3 170099.5 0.00003 22265.5 168985.6

nohz off [1, samples/2] [samples/2 + 1, samples]
samples freq dev max freq dev max
10 6.64956 14.0 18.8 7.10428 2.4 5.1
30 2.87697 13.1 33.0 0.02541 0.1 0.4
100 0.38990 9.9 35.1 0.00502 0.2 0.5
300 0.04733 6.5 42.9 0.00096 0.2 0.5
1000 0.00437 3.7 46.2 0.00023 0.2 0.6
3000 0.00049 2.2 47.1 0.00003 0.2 0.6
10000 0.00004 1.2 47.5 0.00000 0.2 0.6
30000 0.00001 0.8 47.6 0.00000 0.2 0.6
100000 0.00000 0.5 47.6 0.00000 0.2 0.6


3.16-rc5 + two patches from this set:

$ ./test2.sh
nohz on [1, samples/2] [samples/2 + 1, samples]
samples freq dev max freq dev max
10 1.47222 1341.3 2217.8 0.06322 0.2 0.5
30 0.20799 849.5 2448.7 0.06311 0.2 0.6
100 0.04101 492.1 2895.2 0.06311 0.2 0.5
300 0.05660 295.5 3026.1 0.02064 28.3 108.9
1000 0.01994 409.8 2732.1 0.00355 13.7 52.2
3000 0.00477 469.1 3238.9 0.00070 11.0 40.9
10000 0.00081 377.3 3791.6 0.00013 9.4 36.2
30000 0.00016 259.9 4055.7 0.00004 8.9 34.1
100000 0.00003 159.0 4177.2 0.00000 13.7 58.4

nohz off [1, samples/2] [samples/2 + 1, samples]
samples freq dev max freq dev max
10 3.55062 6.2 10.8 0.05730 0.0 0.0
30 0.44672 4.5 14.1 0.05724 0.2 0.5
100 0.03649 2.7 17.4 0.05711 0.2 0.5
300 0.05815 1.7 18.7 0.06313 0.2 0.5
1000 0.06270 1.0 19.1 0.06315 0.2 0.5
3000 0.05720 1.9 19.9 0.02065 1.1 4.1
10000 0.01947 13.5 41.0 0.00339 0.5 1.7
30000 0.00448 17.5 75.9 0.00065 0.3 1.0
100000 0.00078 14.2 101.7 0.00012 0.2 0.7

--
Miroslav Lichvar
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/