Allow specifying instruction set

[erthalion]

Description

Kernel supports few instruction sets [1], and the default one (which is apparently being used at the moment in falco) is going to be the generic or v1, which has certain limitations and requires workarounds. It's possible to instruct llc to search the latest supported instruction set via -mcpu parameter, which generally speaking should result in more compact and potentially more performant generated instructions for the same code. For the support table see great blog post [2] about the topic. The gist for the support is:

v2: Linux v4.14 [3], LLVM v6.0 [4] v3: Linux v5.1 [5], LLVM [6]

Probing is working via performing bpf syscall with various instruction sets and figuring out maximum supported version based on the results. Which means it would work only for the build host, so we need to allow pinning it precisely if needed.

Checklist

• [ ] Investigated and inspected CI test results
• [ ] Updated documentation accordingly

Testing Performed

Local testing with instruction set v2.

[openshift-ci[bot]]

@erthalion: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/ubuntu-1804-lts-ebpf-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test ubuntu-1804-lts-ebpf-integration-tests
ci/prow/sles-15-kernel-module-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test sles-15-kernel-module-integration-tests
ci/prow/cos-85-lts-kernel-module-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test cos-85-lts-kernel-module-integration-tests
ci/prow/cos-dev-ebpf-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test cos-dev-ebpf-integration-tests
ci/prow/cos-stable-ebpf-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test cos-stable-ebpf-integration-tests
ci/prow/sles-12-ebpf-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test sles-12-ebpf-integration-tests
ci/prow/cos-85-lts-ebpf-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test cos-85-lts-ebpf-integration-tests
ci/prow/cos-beta-ebpf-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test cos-beta-ebpf-integration-tests
ci/prow/cos-89-lts-kernel-module-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test cos-89-lts-kernel-module-integration-tests
ci/prow/ubuntu-pro-1804-lts-kernel-module-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test ubuntu-pro-1804-lts-kernel-module-integration-tests
ci/prow/ubuntu-pro-1804-lts-ebpf-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test ubuntu-pro-1804-lts-ebpf-integration-tests
ci/prow/cos-89-lts-ebpf-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test cos-89-lts-ebpf-integration-tests
ci/prow/rhel-sap-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test rhel-sap-integration-tests
ci/prow/rhel-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test rhel-integration-tests
ci/prow/ubuntu-os-integration-tests	74dcb1d53cd083968e2cc90093027c82b5ef3f70	link	true	/test ubuntu-os-integration-tests

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[ghost]

COLLECTOR_TAG=3.12.x-26-g5adabbe03e
COLLECTOR_BUILDER_TAG=cache

Results for Performance Benchmarks on build #

Kernel	Method	Without Collector Time (secs)	With Collector Time (secs)	Baseline median (secs)	Collector median (secs)	PValue
rhel.rhel-7	ebpf	227.502	268.926	163.24	203.43	:green_circle:
rhel.rhel-7	module	99.216	118.99	184.62	210.4	:green_circle:
rhel.rhel-8	ebpf	235.6	245.594	200.85	211.04	:green_circle:
rhel.rhel-8	module	234.81	257.917	174.47	196.72	:green_circle:
ubuntu-os.ubuntu-1804-lts	ebpf	250.682	230.901	189.23	215.86	:red_circle:
ubuntu-os.ubuntu-1804-lts	module	223.94	265.805	183.83	216.45	:green_circle:
ubuntu-os.ubuntu-2004-lts	ebpf	276.051	266.852	234.73	231.91	:green_circle:
ubuntu-os.ubuntu-2004-lts	module	248.769	271.234	224.59	239.44	:green_circle:
ubuntu-os.ubuntu-2204-lts	ebpf	248.663	247.724	213.26	226.83	:green_circle:
ubuntu-os.ubuntu-2204-lts	module	235.638	272.162	215.97	240.73	:green_circle:

[robbycochran]

@erthalion Is this still relevant?

[erthalion]

@robbycochran it is, in the sense that it still could be applied to core_bpf, but has to be evaluated again.