On 01/13/2014 09:51 AM, Richard Cochran wrote: > On Mon, Jan 06, 2014 at 07:57:03PM -0800, John Stultz wrote: >> I still think this is probably 3.15 or later material, but I'd be >> very interested in feedback, thoughts, and testing. > Over the weekend I did a short test of this new approach. I compiled > two kernels, one plain v3.12.7 and one with the proposed fix. The > test was run on three different kernel variants, the current nohz > kernel, the same with nohz=off, and the same but with John's patch. > > I used a simple test script (see below). Using a PCIe express card as > a PHC, the Intel Corporation 82574L, I simply let the this clock run > free (not sync'ed to gps or anything), and then synchronized the Linux > system clock to the PHC using the phc2sys program with a sample rate > of once every 32 seconds. Each of the tests ran for at least three > hours on a system without any other load. > > - Linux 3.12.7-nohz-plain-20140106 nohz-plain.log > - Linux 3.12.7-nohz-plain-20140106 NOHZ=OFF periodic-plain.log > - Linux 3.12.7-nohz-fix-20140106-00001-gd753140 nohz-fix.log > > The performance in the log files as reflected in the clock offset is > summarized in this table. The values are in nanoseconds. > > | | periodic-plain | nohz-fix | nohz-plain | > |---------+----------------+---------------+---------------| > | minimum | -1.599000e+03 | -1.051000e+03 | -5.373700e+04 | > | maximum | +1.311000e+03 | +1.048000e+03 | +6.389500e+04 | > | mean | +9.880240e-02 | -7.747305e+01 | +1.597904e+01 | > | stddev | +4.610021e+02 | +3.960978e+02 | +1.491263e+04 | > > I also made two graphs. > > http://linuxptp.sourceforge.net/nohz-fix/current_nohz.png > http://linuxptp.sourceforge.net/nohz-fix/periodic_vs_fix.png > > (The log files and scripts are also in that directory.) > > So in this test, it looks like the new approach performed at least as > well as using regular, periodic ticks.
That's great to hear! Thanks so much, I really appreciate the testing! And this is with HZ=? If you do get a chance to look again, I'd also be interested if running with nohz=off w/ the fix doesn't show any regression compared to the unmodified nohz=off case. I've been trying to validate the ntpd case to ensure there aren't regressions when there's more erratic steering, but unfortunately got side-tracked with what seems to be an ntpd/virtualization issue. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
