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Diffstat (limited to 'docs/report/introduction/methodology_rca')
| -rw-r--r-- | docs/report/introduction/methodology_rca/index.rst | 6 | ||||
| -rw-r--r-- | docs/report/introduction/methodology_rca/methodology_perpatch_performance_tests.rst | 242 |
2 files changed, 248 insertions, 0 deletions
diff --git a/docs/report/introduction/methodology_rca/index.rst b/docs/report/introduction/methodology_rca/index.rst new file mode 100644 index 0000000000..82c88a3ef9 --- /dev/null +++ b/docs/report/introduction/methodology_rca/index.rst @@ -0,0 +1,6 @@ +Root Cause Analysis +------------------- + +.. toctree:: + + methodology_perpatch_performance_tests diff --git a/docs/report/introduction/methodology_rca/methodology_perpatch_performance_tests.rst b/docs/report/introduction/methodology_rca/methodology_perpatch_performance_tests.rst new file mode 100644 index 0000000000..a3fb4c5938 --- /dev/null +++ b/docs/report/introduction/methodology_rca/methodology_perpatch_performance_tests.rst @@ -0,0 +1,242 @@ +Per-patch performance tests +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Updated for CSIT git commit id: 72b45cfe662107c8e1bb549df71ba51352a898ee. + +A methodology similar to trending analysis is used for comparing performance +before a DUT code change is merged. This can act as a verify job to disallow +changes which would decrease performance without a good reason. + +Existing jobs +````````````` + +VPP is the only project currently using such jobs. +They are not started automatically, must be triggered on demand. +They allow full tag expressions, but some tags are enforced (such as MRR). + +There are jobs available for multiple types of testbeds, +based on various processors. +Their Gerrit triggers words are of the form "perftest-{node_arch}" +where the node_arch combinations currently supported are: +2n-clx, 2n-dnv, 2n-skx, 2n-tx2, 2n-zn2, 3n-dnv, 3n-skx, 3n-tsh. + +Test selection +-------------- + +.. + TODO: Majority of this section is also useful for CSIT verify jobs. Move it somewhere. + +Gerrit trigger line without any additional arguments selects +a small set of test cases to run. +If additional arguments are added to the Gerrit trigger, they are treated +as Robot tag expressions to select tests to run. +While very flexible, this method of test selection also allows the user +to accidentally select too high number of tests, blocking the testbed for days. + +What follows is a list of explanations and recommendations +to help users to select the minimal set of tests cases. + +Verify cycles +_____________ + +When Gerrit schedules multiple jobs to run for the same patch set, +it waits until all runs are complete. +While it is waiting, it is possible to trigger more jobs +(adding runs to the set Gerrit is waiting for), but it is not possible +to trigger more runs for the same job, until Gerrit is done waiting. +After Gerrit is done waiting, it becames possible to trigger +the same job again. + +Example. User triggers one set of tests on 2n-skx and immediately +also triggers other set of tests on 3n-skx. Then the user notices +2n-skx run end early because of a typo in tag expression. +When the user tries to re-trigger 2n-skx (with fixed tag expression), +that comment gets ignored by Jenkins. +Only when 3n-skx job finishes, the user can trigger 2n-skx. + +One comment many jobs +_____________________ + +In the past, the CSIT code which parses for perftest trigger comments +was buggy, which lead to bad behavior (as in selection all performance test, +because "perftest" is also a robot tag) when user included multiple +perftest trigger words in the same comment. + +The worst bugs were fixed since then, but it is still recommended +to use just one trigger word per Gerrit comment, just to be safe. + +Multiple test cases in run +__________________________ + +While Robot supports OR operator, it does not support parentheses, +so the OR operator is not very useful. It is recommended +to use space instead of OR operator. + +Example template: +perftest-2n-skx {tag_expression_1} {tag_expression_2} + +See below for more concrete examples. + +Suite tags +__________ + +Traditionally, CSIT maintains broad Robot tags that can be used to select tests, +for details on existing tags, see +`CSIT Tags <https://github.com/FDio/csit/blob/master/docs/tag_documentation.rst>`_. + +But it is not recommended to use them for test selection, +as it is not that easy to determine how many test cases are selected. + +The recommended way is to look into CSIT repository first, +and locate a specific suite the user is interested in, +and use its suite tag. For example, "ethip4-ip4base" is a suite tag +selecting just one suite in CSIT git repository, +avoiding all scale, container, and other simialr variants. + +Note that CSIT uses "autogen" code generator, +so the robot running in Jenkins has access to more suites +than visible just by looking into CSIT git repository, +so suite tag is not enough to select even the intended suite, +and user still probably wants to narrow down +to a single test case within a suite. + +Fully specified tag expressions +_______________________________ + +Here is one template to select a single test case: +{test_type}AND{nic_model}AND{nic_driver}AND{cores}AND{frame_size}AND{suite_tag} +where the variables are all lower case (so AND operator stands out). + +Currently only one test type is supported by the performance comparison jobs: +"mrr". +The nic_driver options depend on nic_model. For Intel cards "drv_avf" (AVF plugin) +and "drv_vfio_pci" (DPDK plugin) are popular, for Mellanox "drv_rdma_core". +Currently, the performance using "drv_af_xdp" is not reliable enough, so do not use it +unless you are specifically testing for AF_XDP. + +The most popular nic_model is "nic_intel-xxv710", but that is not available +on all testbed types. +It is safe to use "1c" for cores (unless you are suspection multi-core performance +is affected differently) and "64b" for frame size ("78b" for ip6 +and more for dot1q and other encapsulated traffic; +"1518b" is popular for ipsec and other payload-bound tests). + +As there are more test cases than CSIT can periodically test, +it is possible to encounter an old test case that currently fails. +To avoid that, you can look at "job spec" files we use for periodic testing, +for example `this one <https://github.com/FDio/csit/blob/master/docs/job_specs/report_iterative/2n-skx/vpp-mrr-00.md>`_. + +.. + TODO: Explain why "periodic" job spec link lands at report_iterative. + +Shortening triggers +___________________ + +Advanced users may use the following tricks to avoid writing long trigger comments. + +Robot supports glob matching, which can be used to select multiple suite tags at once. + +Not specifying one of 6 parts of the recommended expression pattern +will select all available options. For example not specifying nic_driver +for nic_intel-xxv710 will select all 3 applicable drivers. +You can use NOT operator to reject some options (e.g. NOTdrv_af_xdp), +but beware, with NOT the order matters: +tag1ANDtag2NOTtag3 is not the same as tag1NOTtag3ANDtag2, +the latter is evaluated as tag1AND(NOT(tag3ANDtag2)). + +Beware when not specifying nic_model. As a precaution, +CSIT code will insert the defailt NIC model for the tetsbed used. +Example: Specifying drv_rdma_core without specifying nic_model +will fail, as the default nic_model is nic_intel-xxv710 +which does not support RDMA core driver. + +Complete example +________________ + +A user wants to test a VPP change which may affect load balance whith bonding. +Searching tag documentation for "bonding" finds LBOND tag and its variants. +Searching CSIT git repository (directory tests/) finds 8 suite files, +all suited only for 3-node testbeds. +All suites are using vhost, but differ by the forwarding app inside VM +(DPDK or VPP), by the forwarding mode of VPP acting as host level vswitch +(MAC learning or cross connect), and by the number of DUT1-DUT2 links +available (1 or 2). + +As not all NICs and testbeds offer enogh ports for 2 parallel DUT-DUT links, +the user looks at `testbed specifications <https://github.com/FDio/csit/tree/master/topologies/available>`_ +and finds that only x710 NIC on 3n-skx testbed matches the requirements. +Quick look into the suites confirm the smallest frame size is 64 bytes +(despite DOT1Q robot tag, as the encapsulation does not happen on TG-DUT links). +It is ok to use just 1 physical core, as 3n-skx has hyperthreading enabled, +so VPP vswitch will use 2 worker threads. + +The user decides the vswitch forwarding mode is not important +(so choses cross connect as that has less CPU overhead), +but wants to test both NIC drivers (not AF_XDP), both apps in VM, +and both 1 and 2 parallel links. + +After shortening, this is the trigger comment fianlly used: +perftest-3n-skx mrrANDnic_intel-x710AND1cAND64bAND?lbvpplacp-dot1q-l2xcbase-eth-2vhostvr1024-1vm*NOTdrv_af_xdp + +Basic operation +``````````````` + +The job builds VPP .deb packages for both the patch under test +(called "current") and its parent patch (called "parent"). + +For each test (from a set defined by tag expression), +both builds are subjected to several trial measurements (BMRR). +Measured samples are grouped to "parent" sequence, +followed by "current" sequence. The same Minimal Description Length +algorithm as in trending is used to decide whether it is one big group, +or two smaller gropus. If it is one group, a "normal" result +is declared for the test. If it is two groups, and current average +is less then parent average, the test is declared a regression. +If it is two groups and current average is larger or equal, +the test is declared a progression. + +The whole job fails (giving -1) if some trial measurement failed, +or if any test was declared a regression. + +Temporary specifics +``````````````````` + +The Minimal Description Length analysis is performed by +CSIT code equivalent to jumpavg-0.1.3 library available on PyPI. + +In hopes of strengthening of signal (code performance) compared to noise +(all other factors influencing the measured values), several workarounds +are applied. + +In contrast to trending, trial duration is set to 10 seconds, +and only 5 samples are measured for each build. +Both parameters are set in ci-management. + +This decreases sensitivity to regressions, but also decreases +probability of false positives. + +Console output +`````````````` + +The following information as visible towards the end of Jenkins console output, +repeated for each analyzed test. + +The original 5 values are visible in order they were measured. +The 5 values after processing are also visible in output, +this time sorted by value (so people can see minimum and maximum). + +The next output is difference of averages. It is the current average +minus the parent average, expressed as percentage of the parent average. + +The next three outputs contain the jumpavg representation +of the two groups and a combined group. +Here, "bits" is the description length; for "current" sequence +it includes effect from "parent" average value +(jumpavg-0.1.3 penalizes sequences with too close averages). + +Next, a sentence describing which grouping description is shorter, +and by how much bits. +Finally, the test result classification is visible. + +The algorithm does not track test case names, +so test cases are indexed (from 0). |