git: 76186d25a4 - main - Status/2024Q2/zcond.adoc: Add report

The branch main has been updated by salvadore:

URL: https://cgit.FreeBSD.org/doc/commit/?id=76186d25a4627438dae2403a108d7866d0c9b0ef

commit 76186d25a4627438dae2403a108d7866d0c9b0ef
Author:     Marko Vlaić <mvlaic@freebsd.org>
AuthorDate: 2024-07-07 13:14:15 +0000
Commit:     Lorenzo Salvadore <salvadore@FreeBSD.org>
CommitDate: 2024-07-07 13:16:05 +0000

    Status/2024Q2/zcond.adoc: Add report
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+=== A low-cost conditional execution mechanism
+
+Links: +
+link:https://wiki.freebsd.org/SummerOfCode2024Projects/ZeroCostConditionalExecutionMechanism[FreeBSD wiki] URL: https://wiki.freebsd.org/SummerOfCode2024Projects/ZeroCostConditionalExecutionMechanism[] +
+
+Contact: Marko Vlaić <mvlaic@freebsd.org>
+Contact: Bojan Novković (mentor) <bnovkov@freebsd.org>
+
+This project aims to implement a low-cost conditional execution mechanism, similar to the `static_key` interface in Linux.
+The current working name is `zcond`, as in zero-cost conditional.
+The idea is to reduce the overhead of rarely used features in performance sensitive kernel code paths.
+Specifically, code blocks of the following, simple structure, are targeted:
+
+[source, c]
+----
+if(some_global_flag == true) {
+    do_some_additional_task();
+}
+----
+
+A block like this can cause performance overhead in a frequently executed piece of code.
+
+The motivating use case for the mechanism is tracing (as outlined here in the link:https://wiki.freebsd.org/SummerOfCodeIdeas#Unified_kernel_tracing_interface[wiki]), but the project will identify more areas where this mechanism could be applied.
+
+The backbone of the mechanism is runtime instruction hot patching, making it highly architecture dependent.
+Great care has to be given to security, because kernel instructions are overwritten at runtime.
+More details and some implementation ideas can be found in the project proposal on the link:https://wiki.freebsd.org/SummerOfCode2024Projects/ZeroCostConditionalExecutionMechanism[project wiki page].
+More documents describing the implementation and design decisions will be produced, as the project moves along.
+
+The goal of the project is to produce a working implementaion of the mechanism for the x86-64 architecture.
+It will then be applied to an existing piece of kernel code and benchmarked.
+If the benchmark results come out positive, it will be ported to other architectures.
+
+This project is a part of the link:https://summerofcode.withgoogle.com/[Google Summer of Code 2024.].
+The project is still in its early stages, but any feedback would be highly appreciated.
+
+==== Help wanted
+* General feedback on the mechanism, API and implementation
+* More use cases besides tracing are welcome
+* Code review
+* Name suggestions
+
+Sponsor: Google LLC (GSoC 2024)