Hi James, Interesting results, but did you do any tests with a NUMA system? IIUC the original report was from a dual socket setup, and that'd presumably be the standard setup for most folks (both OSD server and client side). Cheers, On 20 February 2015 at 20:07, James Page <james.page@xxxxxxxxxx> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA256 > > Hi All > > The Ubuntu Kernel team have spent the last few weeks investigating the > apparent performance disparity between RHEL 7 and Ubuntu 14.04; we've > focussed efforts in a few ways (see below). > > All testing has been done using the latest Firefly release. > > 1) Base network latency > > Jay Vosburgh looked at the base network latencies between RHEL 7 and > Ubuntu 14.04; under default install, RHEL actually had slightly worse > latency than Ubuntu due to the default enablement of a firewall; > disabling this brought latency back inline between the two distributions: > > OS rtt min/avg/max/mdev > Ubuntu 14.04 (3.13) 0.013/0.016/0.018/0.005 ms > RHEL7 (3.10) 0.010/0.018/0.025/0.005 ms > > ...base network latency is pretty much the same. > > This testing was performed on a matched pair of Dell Poweredge R610's, > configured with a single 4 core CPU and 8G of RAM. > > 2) Latency and performance in Ceph using Rados bench > > Colin King spent a number of days testing and analysing results using > rados bench against a single node ceph deployment, configured with a > single memory backed OSD, to see if we could reproduce the disparities > reported. > > He ran 120 second OSD benchmarks on RHEL 7 as well as Ubuntu 14.04 LTS > with a selection of kernels including 3.10 vanilla, 3.13.0-44 (release > kernel), 3.16.0-30 (utopic HWE kernel), 3.18.0-12 (vivid HWE kernel) > and 3.19-rc6 with 1, 16 and 128 client threads. The data collected is > available at [0]. > > Each round of tests consisted of 15 runs, from which we computed > average latency, latency deviation and latency distribution: > >> 120 second x 1 thread > > Results all seem to cluster around 0.04->0.05ms, with RHEL 7 averaging > at 0.044 and recent Ubuntu kernels at 0.036-0.037ms. The older 3.10 > kernel in RHEL 7 does have some slightly higher average latency. > >> 120 second x 16 threads > > Results all seem to cluster around 0.6-0.7ms. 3.19.0-rc6 had a couple > of 1.4ms outliers which pushed it out to be worse than RHEL 7. On the > whole Ubuntu 3.10-3.18 kernels are better than RHEL 7 by ~0.1ms. RHEL > shows a far higher standard deviation, due to the bimodal latency > distribution, which from the casual observer may appear to be more > "jittery". > >> 120 second x 128 threads > > Later kernels show up to have less standard deviation than RHEL 7, so > that shows perhaps less jitter in the stats than RHEL 7's 3.10 kernel. > With this many threads pounding the test, we get a wider spread of > latencies and it is hard to tell any kind of latency distribution > patterns with just 15 rounds because of the large amount of latency > jitter. All systems show a latency of ~ 5ms. Taking into > consideration the amount of jitter, we think these results do not make > much sense unless we repeat these tests with say 100 samples. > > 3) Conclusion > > We’ve have not been able to show any major anomalies in Ceph on Ubuntu > compared to RHEL 7 when using memstore. Our current hypothesis is that > one needs to run the OSD bench stressor many times to get a fair capture > of system latency stats. The reason for this is: > > * Latencies are very low with memstore, so any small jitter in > scheduling etc will show up as a large distortion (as shown by the large > standard deviations in the samples). > > * When memstore is heavily utilized, memory pressure causes the system > to page heavily and so we are subject to the nature of perhaps delays on > paging that cause some latency jitters. Latency differences may be just > down to where a random page is in memory or in swap, and with memstore > these may cause the large perturbations we see when running just a > single test. > > * We needed to make *many* tens of measurements to get a typical idea of > average latency and the latency distributions. Don't trust the results > from just one test > > * We ran the tests with a pool configured to 100 pgs and 100 pgps [1]. > One can get different results with different placement group configs. > > I've CC'ed both Colin and Jay on this mail - so if anyone has any > specific questions about the testing they can chime in with responses. > > Regards > > James > > [0] http://kernel.ubuntu.com/~cking/.ceph/ceph-benchmarks.ods > [1] http://ceph.com/docs/master/rados/configuration/pool-pg-config-ref/ > > - -- > James Page > Ubuntu and Debian Developer > james.page@xxxxxxxxxx > jamespage@xxxxxxxxxx > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1 > > iQIcBAEBCAAGBQJU5vlrAAoJEL/srsug59jDMvAQAIhSR4GFTXNc4RLpHtLT6h/X > K5uyauKZGtL+wqtPKRfsXqbbUw9I5AZDifQuOEJ0APccLIPbgqxEN3d2uht/qygH > G8q2Ax+M8OyZz07yqTitnD4JV3RmL8wNHUveWPLV0gs2TzBBYwP1ywExbRPed3PY > cfDrszgkQszA/JwT5W5YNf1LZc+5VpOEFrTiLIaRzUDoxg7mm6Hwr3XT8OFjZhjm > LSenKREHtrKKWoBh+OKTvuCUnHzEemK+CiwwRbNQ8l7xbp71wLyS08NpSB5C1y70 > 7uft+kP6XOGE9AKLvsdEL1PIXHfeKNonBEN5mO6nsXIW+MQzou01zHgDtne7AxDA > 5OebQJfJtArmKt78WHuVg7h8gPcIRTRSW43LqJiADnIHL8fnZxj2v5yDiUQj7isw > nYWXEJ3rR7mlVgydN34KQ7gpVWmGjhrVb8N01+zYOMAaTBnekldHdueEAXR07eU0 > PXiP9aOZiAxbEnDiJmreehjCuNFTagQqNeECRIHssSacfQXPxVljaImvuSfrxf8i > myQLzftiObINTIHSN4TVDKMyveYrU2hILCKfYuxnSJh29j35wsRSeftjntOEyHai > RDnrLD3fCPk4h3hCY6l60nqu9MQfbgdSB/FItvhiBGYqXvGb4+wuBeU9RT9SwG8N > XPih7nLNvqDNw38IkkDN > =qcvG > -----END PGP SIGNATURE----- > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Cheers, ~Blairo -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
