feat(bisect): introduce scripts for VPP bisecting

+ Parsing common with per-patch job is moved to a library.

Ticket: CSIT-1618

Change-Id: I185bea084a29e6a37ef94e9da42b192a6a81fc17
Signed-off-by: Vratko Polak <vrpolak@cisco.com>

3 files changed, 266 insertions, 1 deletions

diff --git a/resources/libraries/bash/entry/bisect.sh b/resources/libraries/bash/entry/bisect.sh
new file mode 100644
index 0000000000..d5cb1d51ba
--- /dev/null
+++ b/resources/libraries/bash/entry/bisect.sh
@@ -0,0 +1,188 @@
+#!/usr/bin/env bash
+
+# Copyright (c) 2023 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -exuo pipefail
+
+# This entry script does not change which CSIT branch is used,
+# use "with_oper_for_vpp.sh" wrapper for that.
+#
+# This script is to be used for locating performance regressions
+# (or breakages, or progressions, or fixes).
+# It uses "git bisect" commands on the VPP repository,
+# between the triggered VPP patch and a commit specified in the first argument
+# of the gerrit comment text.
+# The other arguments are used as tag expressions for selecting tests as usual.
+# Many different result types are supported.
+#
+# Logs are present in the archive directory, but usually the main output
+# is the offending commit as identified by "git bisect", visible in console.
+#
+# While selecting just one testcase is the intended use,
+# this script should be able to deal with multiple testcases as well,
+# grouping all the values together. This usually inflates
+# the standard deviation, but it is not clear how that affects the bisection.
+#
+# For the bisection decision, jumpavg library is used,
+# deciding whether shorter description is achieved by forcefully grouping
+# the middle results with the old, or with the new ones.
+# If the shortest description is achieved with 3 separate groups,
+# bisect interval focuses on biggest relative change
+# (with respect to pairwise maximum).
+#
+# If a test fails, an artificial result is used to distinguish
+# from normal results. Currently, the value 1.0, with the multiplicity of 4.
+#
+# Note that if there was a VPP API change that affects tests in the interval,
+# there frequently is no good way for single CSIT commit to work there.
+# You can try manually reverting the CSIT changes to make tests pass,
+# possibly needing to search over multiple subintervals.
+# Using and older CSIT commit (possibly cherry-picking the bisect Change
+# if it was not present in CSIT compatible with old enough VPP builds)
+# is the fastest solution; but beware of CSIT-induced performance effects
+# (e.g. TRex settings).
+#
+# If a regression happens during a subinterval where the test fails
+# due to a bug in VPP, you may try to create a new commit chain
+# with the fix cherry-picked to the start of the interval.
+# Do not do that as a chain in Gerrit, it would be long and Gerrit will refuse
+# edits of already merged Changes.
+# Instead, add a block of bash code to do the manipulation
+# on local git history between checkout and bisect.
+#
+# At the start, the script executes first bisect iteration in an attempt
+# to avoid work if the search interval has only one commit (or is invalid).
+# Only when the work is needed, earliest and latest commits are built
+# and tested. Branches "earliest", "middle" and "latest" are temporarily created
+# as a way to remember which commits to check out.
+#
+# Test results are parsed from json files,
+# symlinks are used to tell python script which results to compare.
+#
+# Assumptions:
+# + There is a directory holding VPP repo with patch under test checked out.
+# + It contains csit subdirectory with CSIT code to use (this script is there).
+# + Everything needed to build VPP is already installed locally.
+# Consequences:
+# + Working directory is switched to the VPP repo root.
+# + At the end, VPP repo has checked out and built some commit,
+#   as chosen by "git bisect".
+# + Directories build_root, build and csit are reset during the run.
+# + The following directories (relative to VPP repo) are (re)created:
+# ++ csit_{earliest,middle,latest}, build_{earliest,latest},
+# ++ archive, csit/archive, csit/download_dir.
+# + Symlinks csit_{early,late,mid} are also created.
+# Arguments:
+# - ${1} - If present, override JOB_NAME to simplify manual usage.
+
+# "set -eu" handles failures from the following two lines.
+BASH_ENTRY_DIR="$(dirname $(readlink -e "${BASH_SOURCE[0]}"))"
+BASH_FUNCTION_DIR="$(readlink -e "${BASH_ENTRY_DIR}/../function")"
+source "${BASH_FUNCTION_DIR}/common.sh" || {
+    echo "Source failed." >&2
+    exit 1
+}
+source "${BASH_FUNCTION_DIR}/per_patch.sh" || die "Source failed."
+# Cleanup needs ansible.
+source "${BASH_FUNCTION_DIR}/ansible.sh" || die "Source failed."
+common_dirs || die
+check_prerequisites || die
+set_perpatch_vpp_dir || die
+get_test_code "${1-}" || die
+get_test_tag_string || die
+# Unfortunately, git bisect only works at the top of the repo.
+cd "${VPP_DIR}" || die
+
+# Save the current commit.
+git checkout -b "latest"
+# Save the lower bound commit.
+git checkout -b "earliest"
+git reset --hard "${GIT_BISECT_FROM}"
+
+# This is the place for custom code manipulating local git history.
+
+#git checkout -b "alter"
+#...
+#git checkout "latest"
+#git rebase "alter" || git rebase --skip
+#git branch -D "alter"
+
+git bisect start || die
+# TODO: Can we add a trap for "git bisect reset" or even "deactivate",
+# without affecting the inner trap for unreserve and cleanup?
+git checkout "latest"
+git status || die
+git describe || die
+git bisect new || die
+# Performing first iteration early to avoid testing or even building.
+git checkout "earliest" || die "Failed to checkout earliest commit."
+git status || die
+git describe || die
+# The first iteration.
+git bisect old | tee "git.log" || die "Invalid bisect interval?"
+git checkout -b "middle" || die "Failed to create branch: middle"
+git status || die
+git describe || die
+if head -n 1 "git.log" | cut -b -11 | fgrep -q "Bisecting:"; then
+    echo "Building and testing initial bounds."
+else
+    echo "Single commit, no work needed."
+    exit 0
+fi
+# Building latest first, good for avoiding DPDK rebuilds.
+git checkout "latest" || die "Failed to checkout latest commit."
+build_vpp_ubuntu "LATEST" || die
+set_aside_build_artifacts "latest" || die
+git checkout "earliest" || die "Failed to checkout earliest commit."
+git status || die
+git describe || die
+build_vpp_ubuntu "EARLIEST" || die
+set_aside_build_artifacts "earliest" || die
+git checkout "middle" || die "Failed to checkout middle commit."
+git branch -D "earliest" "latest" || die "Failed to remove branches."
+# Done with repo manipulation for now, testing commences.
+initialize_csit_dirs "earliest" "middle" "latest" || die
+set_perpatch_dut || die
+select_topology || die
+select_arch_os || die
+activate_virtualenv "${VPP_DIR}" || die
+generate_tests || die
+archive_tests || die
+
+# TODO: Does it matter which build is tested first?
+
+select_build "build_earliest" || die
+check_download_dir || die
+reserve_and_cleanup_testbed || die
+run_robot || die
+move_test_results "csit_earliest" || die
+ln -s -T "csit_earliest" "csit_early" || die
+
+# Explicit cleanup, in case the previous test left the testbed in a bad shape.
+ansible_playbook "cleanup"
+
+select_build "build_latest" || die
+check_download_dir || die
+run_robot || die
+move_test_results "csit_latest" || die
+ln -s -T "csit_latest" "csit_late" || die
+untrap_and_unreserve_testbed || die
+
+# See function documentation for the logic in the loop.
+main_bisect_loop || die
+# In worst case, the middle branch is still checked out.
+# TODO: Is there a way to ensure "middle" branch is always deleted?
+git branch -D "middle" || true
+# Delete symlinks to prevent duplicate archiving.
+rm -vrf "csit_early" "csit_late" "csit_mid"
diff --git a/resources/libraries/bash/function/common.sh b/resources/libraries/bash/function/common.sh
index 44149ca6e1..c2b169f550 100644
--- a/resources/libraries/bash/function/common.sh
+++ b/resources/libraries/bash/function/common.sh
@@ -290,7 +290,7 @@ function compose_robot_arguments () {
         *"device"*)
             ROBOT_ARGS+=("--suite" "tests.${DUT}.device")
             ;;
-        *"perf"*)
+        *"perf"* | *"bisect"*)
             ROBOT_ARGS+=("--suite" "tests.${DUT}.perf")
             ;;
         *)
@@ -557,6 +557,8 @@ function get_test_tag_string () {
     # Variables set:
     # - TEST_TAG_STRING - The string following trigger word in gerrit comment.
     #   May be empty, or even not set on event types not adding comment.
+    # - GIT_BISECT_FROM - If bisecttest, the commit hash to bisect from.
+    #   Else not set.
     # Variables exported optionally:
     # - GRAPH_NODE_VARIANT - Node variant to test with, set if found in trigger.
 
@@ -566,6 +568,10 @@ function get_test_tag_string () {
 
     if [[ "${GERRIT_EVENT_TYPE-}" == "comment-added" ]]; then
         case "${TEST_CODE}" in
+            # Order matters, bisect job contains "perf" in its name.
+            *"bisect"*)
+                trigger="bisecttest"
+                ;;
             *"device"*)
                 trigger="devicetest"
                 ;;
@@ -591,6 +597,18 @@ function get_test_tag_string () {
             comment=$(fgrep "${trigger}" <<< "${comment}" || true)
             TEST_TAG_STRING=$("${cmd[@]}" <<< "${comment}" || true)
         fi
+        if [[ "${trigger}" == "bisecttest" ]]; then
+            # Intentionally without quotes, so spaces delimit elements.
+            test_tag_array=(${TEST_TAG_STRING}) || die "How could this fail?"
+            # First "argument" of bisecttest is a commit hash.
+            GIT_BISECT_FROM="${test_tag_array[0]}" || {
+                die "Bisect job requires commit hash."
+            }
+            # Update the tag string (tag expressions only, no commit hash).
+            TEST_TAG_STRING="${test_tag_array[@]:1}" || {
+                die "Bisect job needs a single test, no default."
+            }
+        fi
         if [[ -n "${TEST_TAG_STRING-}" ]]; then
             test_tag_array=(${TEST_TAG_STRING})
             if [[ "${test_tag_array[0]}" == "icl" ]]; then
diff --git a/resources/libraries/bash/function/per_patch.sh b/resources/libraries/bash/function/per_patch.sh
index b9680a1560..44bd57da80 100644
--- a/resources/libraries/bash/function/per_patch.sh
+++ b/resources/libraries/bash/function/per_patch.sh
@@ -110,6 +110,65 @@ function initialize_csit_dirs () {
 }
 
 
+function main_bisect_loop () {
+
+    # Perform the iterative part of bisect entry script.
+    #
+    # The logic is too complex to remain in the entry script.
+    #
+    # At the start, the loop assumes git bisect old/new has just been executed,
+    # and verified more iterations are needed.
+    # The iteration cleans the build directory and builds the new mid commit.
+    # Then, testbed is reserved, tests run, and testbed unreserved.
+    # Results are moved from default to archive location
+    # (indexed by iteration number) and analyzed.
+    # The new adjective ("old" or "new") is selected,
+    # and git bisect with the adjective is executed.
+    # The symlinks csit_early and csit_late are updated to tightest bounds.
+    # The git.log file is examined and if the bisect is finished, loop ends.
+
+    iteration=0
+    while true
+    do
+        let iteration+=1
+        git clean -dffx "build"/ "build-root"/ || die
+        build_vpp_ubuntu "MIDDLE" || die
+        select_build "build-root" || die
+        check_download_dir || die
+        reserve_and_cleanup_testbed || die
+        run_robot || die
+        move_test_results "csit_middle/${iteration}" || die
+        untrap_and_unreserve_testbed || die
+        rm -vf "csit_mid" || die
+        ln -s -T "csit_middle/${iteration}" "csit_mid" || die
+        set +e
+        python3 "${TOOLS_DIR}/integrated/compare_bisect.py"
+        bisect_rc="${?}"
+        set -e
+        if [[ "${bisect_rc}" == "3" ]]; then
+            adjective="new"
+            rm -v "csit_late" || die
+            ln -s -T "csit_middle/${iteration}" "csit_late" || die
+        elif [[ "${bisect_rc}" == "0" ]]; then
+            adjective="old"
+            rm -v "csit_early" || die
+            ln -s -T "csit_middle/${iteration}" "csit_early" || die
+        else
+            die "Unexpected return code: ${bisect_rc}"
+        fi
+        git bisect "${adjective}" | tee "git.log" || die
+        git describe || die
+        git status || die
+        if head -n 1 "git.log" | cut -b -11 | fgrep -q "Bisecting:"; then
+            echo "Still bisecting..."
+        else
+            echo "Bisecting done."
+            break
+        fi
+    done
+}
+
+
 function move_test_results () {
 
     # Arguments: