gnufx

Actually, one caveat is that GCC's optimization info can be rather inscrutable because it's in terms of compiler internal nomenclature. That's a definite area for improvement (or compiling some sort of key to it).

Indeed, GCC optimizes well. Last time I ran a set of Fortran benchmarks, the geometric mean for them was competitive with other compilers on multiple architectures, and some of the benchmarks could have been sped up considerably with specific compiler options or by re-writing a function sacrificing numerical equivalence, which the Intel compiler seemed to do itself.

Vectorization doesn't imply SIMD, of course. The first vectorizing compilers were for CDC(?) systems long before SIMD. Today you have SVE in Arm, for instance, distinct from SIMD Neon.

Anyway, I'm familiar with optimizing numeric loops in C (and Fortran) rather than Rust. I've rarely seen simply using SIMD intrinsics work where GCC auto-vectorization didn't with the same semantics (like numeric equivalence in reductions). In most cases you can get away with -fassociative-math, of course, and not sacrifice peak performance, e.g. BLIS passes its extensive tests with it on, but you should check, of course. (GCC also documents the option as necessary to get Arm (Neon?) to vectorize at all.) Most of the time when people tell you how much better the Itel compiler is, it's because it incorrectly defaults to something like -funsafe-math.

Regardless, GCC (like other compilers) will tell you about vectorization with the -fopt-info- options without examining assembler, and you can have some surprises. For instance, you use unsigned in C for loop indices that you know are positive, and see failed vectorization due to "loop not affine", because of C's overflow semantics; use signed types instead.

There's another reason for using properly-optimized numerical libraries (typically BLAS), is that, at least for level three (matrix-matrix) operations. Even if you get the blocking right for the memory hierarchy, you typically won't get peak performance just with vectorization because tricky preloading is needed for the inner loops.

The latest page cache-related LPE, even though it's not Thursday night (here). EL9 kernels don't have the modules enabled, and the PoC doesn't build on Debian 13 or Ubuntu 24.04, whether or not that means they're safe.

You might not have root on an organizational "managed" system.

Any university or national HPC system as I'd understand the term is multi-user.

There are also things like the extensive high energy physics WLCG compute federation, which is somewhat different, but can potentially be compromised quickly at large scale. For the original copy-fail we didn't want to drain our WLCG Alma9 cluster, or just kill all the jobs like the university HPC system. We got eBPF mitigation in place within a couple of hours, relieved the exploit signature wasn't in logs from the night before. That would have been done earlier if Proofpoint hadn't bounced the forwarded oss-security article as "contains malware"; sigh.

Yes, but its authN components only act locally, and PAM is optional for sshd. It can/does call out to network services like Kerberos/LDAP given a password, of course, but I was thinking of network authN connected directly with OIDC somehow, for which I don't know a mechanism in vanilla OpenSSH. (I don't know what Authentik does for this -- I could imagine it's behind the scenes somehow.) I should probably look it up sometime.

I'm happy for anyone who doesn't have MS Windows/Active Directory -- so Kerberos -- in their organization, but I'd need (Free)IPA or similar for user/access management anyway. Certificates are an extra layer of SSH-specific complexity, which concerns me for security even if it doesn't involve some third party. MFA is needed once a day, say, for SSO to all Kerberized services. [As I understand it, "managing an OIDC IdP" includes shipping the contents of Active Directory to Entra, heaven help us.]

> Setting up Kerberos in 2026 feels somewhat close to malpractice to me.

Microsoft (if that means anything, but they've done good work) and Red Hat obviously disagree, along with decades' experience. It is malpractice not to secure NFS mounts (and other network filesystems with sensitive data), and that means Kerberos.

Yes, FreeIPA is Kerberos+LDAP+X.509 CA, and GSSAPI is in OpenSSH (normally with the key exchange patch). SSSD is a local mechanism, not network authentication. I mentioned authorized keys distribution mechanisms elsewhere, but I was thinking authentication (c.f. OIDC), not authorization.