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diff --git a/resources/libraries/bash/entry/bisect.sh b/resources/libraries/bash/entry/bisect.sh
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+#!/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"