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Date: Sat, 27 Jul 2013 08:43:15 +0200 From: Daniel Lezcano <daniel.lezcano@...aro.org> To: Jeremy Eder <jeder@...hat.com> CC: linux-kernel@...r.kernel.org, rafael.j.wysocki@...el.com, riel@...hat.com, youquan.song@...el.com, paulmck@...ux.vnet.ibm.com, arjan@...ux.intel.com, len.brown@...el.com Subject: Re: RFC: revert request for cpuidle patches e11538d1 and 69a37bea On 07/26/2013 07:33 PM, Jeremy Eder wrote: > Hello, > > We believe we've identified a particular commit to the cpuidle code that > seems to be impacting performance of variety of workloads. The simplest way to > reproduce is using netperf TCP_RR test, so we're using that, on a pair of > Sandy Bridge based servers. We also have data from a large database setup > where performance is also measurably/positively impacted, though that test > data isn't easily share-able. > > Included below are test results from 3 test kernels: Is the system tickless or with a periodic tick ? > kernel reverts > ----------------------------------------------------------- > 1) vanilla upstream (no reverts) > > 2) perfteam2 reverts e11538d1f03914eb92af5a1a378375c05ae8520c > > 3) test reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4 > e11538d1f03914eb92af5a1a378375c05ae8520c > > In summary, netperf TCP_RR numbers improve by approximately 4% after > reverting 69a37beabf1f0a6705c08e879bdd5d82ff6486c4. When > 69a37beabf1f0a6705c08e879bdd5d82ff6486c4 is included, C0 residency never > seems to get above 40%. Taking that patch out gets C0 near 100% quite > often, and performance increases. > > The below data are histograms representing the %c0 residency @ 1-second > sample rates (using turbostat), while under netperf test. > > - If you look at the first 4 histograms, you can see %c0 residency almost > entirely in the 30,40% bin. > - The last pair, which reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4, > shows %c0 in the 80,90,100% bins. > > Below each kernel name are netperf TCP_RR trans/s numbers for the > particular kernel that can be disclosed publicly, comparing the 3 test > kernels. We ran a 4th test with the vanilla kernel where we've also set > /dev/cpu_dma_latency=0 to show overall impact boosting single-threaded > TCP_RR performance over 11% above baseline. > > 3.10-rc2 vanilla RX + c0 lock (/dev/cpu_dma_latency=0): > TCP_RR trans/s 54323.78 > > ----------------------------------------------------------- > 3.10-rc2 vanilla RX (no reverts) > TCP_RR trans/s 48192.47 > > Receiver %c0 > 0.0000 - 10.0000 [ 1]: * > 10.0000 - 20.0000 [ 0]: > 20.0000 - 30.0000 [ 0]: > 30.0000 - 40.0000 [ 59]: > *********************************************************** > 40.0000 - 50.0000 [ 1]: * > 50.0000 - 60.0000 [ 0]: > 60.0000 - 70.0000 [ 0]: > 70.0000 - 80.0000 [ 0]: > 80.0000 - 90.0000 [ 0]: > 90.0000 - 100.0000 [ 0]: > > Sender %c0 > 0.0000 - 10.0000 [ 1]: * > 10.0000 - 20.0000 [ 0]: > 20.0000 - 30.0000 [ 0]: > 30.0000 - 40.0000 [ 11]: *********** > 40.0000 - 50.0000 [ 49]: > ************************************************* > 50.0000 - 60.0000 [ 0]: > 60.0000 - 70.0000 [ 0]: > 70.0000 - 80.0000 [ 0]: > 80.0000 - 90.0000 [ 0]: > 90.0000 - 100.0000 [ 0]: > > ----------------------------------------------------------- > 3.10-rc2 perfteam2 RX (reverts commit > e11538d1f03914eb92af5a1a378375c05ae8520c) > TCP_RR trans/s 49698.69 > > Receiver %c0 > 0.0000 - 10.0000 [ 1]: * > 10.0000 - 20.0000 [ 1]: * > 20.0000 - 30.0000 [ 0]: > 30.0000 - 40.0000 [ 59]: > *********************************************************** > 40.0000 - 50.0000 [ 0]: > 50.0000 - 60.0000 [ 0]: > 60.0000 - 70.0000 [ 0]: > 70.0000 - 80.0000 [ 0]: > 80.0000 - 90.0000 [ 0]: > 90.0000 - 100.0000 [ 0]: > > Sender %c0 > 0.0000 - 10.0000 [ 1]: * > 10.0000 - 20.0000 [ 0]: > 20.0000 - 30.0000 [ 0]: > 30.0000 - 40.0000 [ 2]: ** > 40.0000 - 50.0000 [ 58]: > ********************************************************** > 50.0000 - 60.0000 [ 0]: > 60.0000 - 70.0000 [ 0]: > 70.0000 - 80.0000 [ 0]: > 80.0000 - 90.0000 [ 0]: > 90.0000 - 100.0000 [ 0]: > > ----------------------------------------------------------- > 3.10-rc2 test RX (reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4 and > e11538d1f03914eb92af5a1a378375c05ae8520c) > TCP_RR trans/s 47766.95 > > Receiver %c0 > 0.0000 - 10.0000 [ 1]: * > 10.0000 - 20.0000 [ 1]: * > 20.0000 - 30.0000 [ 0]: > 30.0000 - 40.0000 [ 27]: *************************** > 40.0000 - 50.0000 [ 2]: ** > 50.0000 - 60.0000 [ 0]: > 60.0000 - 70.0000 [ 2]: ** > 70.0000 - 80.0000 [ 0]: > 80.0000 - 90.0000 [ 0]: > 90.0000 - 100.0000 [ 28]: **************************** > > Sender: > 0.0000 - 10.0000 [ 1]: * > 10.0000 - 20.0000 [ 0]: > 20.0000 - 30.0000 [ 0]: > 30.0000 - 40.0000 [ 11]: *********** > 40.0000 - 50.0000 [ 0]: > 50.0000 - 60.0000 [ 1]: * > 60.0000 - 70.0000 [ 0]: > 70.0000 - 80.0000 [ 3]: *** > 80.0000 - 90.0000 [ 7]: ******* > 90.0000 - 100.0000 [ 38]: ************************************** > > These results demonstrate gaining back the tendency of the CPU to stay in > more responsive, performant C-states (and thus yield measurably better > performance), by reverting commit 69a37beabf1f0a6705c08e879bdd5d82ff6486c4. > > While taking into account the changing landscape with regards to CPU > governors, and both P- and C-states, we think that a single-thread should > still be able to achieve maximum performance. With the current upstream > code base, workloads with a low number of "hot" threads are not able to > achieve maximum performance "out of the box". > > Also recently, Intel's LAD has posted upstream performance results that > include an interesting column with their table of results. See upstream > commit 0a4db187a999, column #3 within the "Performance numbers" table. It > seems known, even within Intel, that the deeper C-states incur a cost too > high to bear, as they've explicitly tested restricting the CPU to higher > c-states of C0,1. > > -- Jeremy Eder > -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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