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Re: [RFC PATCH 25/28] x86: Use PIE codegen for the core kernel
- To: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- From: Uros Bizjak <ubizjak@xxxxxxxxx>
- Date: Sun, 6 Oct 2024 10:06:33 +0200
- Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>, Ard Biesheuvel <ardb@xxxxxxxxxx>, Ard Biesheuvel <ardb+git@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, Andy Lutomirski <luto@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Dennis Zhou <dennis@xxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Christoph Lameter <cl@xxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Masahiro Yamada <masahiroy@xxxxxxxxxx>, Kees Cook <kees@xxxxxxxxxx>, Nathan Chancellor <nathan@xxxxxxxxxx>, Keith Packard <keithp@xxxxxxxxxx>, Justin Stitt <justinstitt@xxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>, Namhyung Kim <namhyung@xxxxxxxxxx>, Jiri Olsa <jolsa@xxxxxxxxxx>, Ian Rogers <irogers@xxxxxxxxxx>, Adrian Hunter <adrian.hunter@xxxxxxxxx>, Kan Liang <kan.liang@xxxxxxxxxxxxxxx>, linux-doc@xxxxxxxxxxxxxxx, linux-pm@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-efi@xxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, linux-sparse@xxxxxxxxxxxxxxx, linux-kbuild@xxxxxxxxxxxxxxx, linux-perf-users@xxxxxxxxxxxxxxx, rust-for-linux@xxxxxxxxxxxxxxx, llvm@xxxxxxxxxxxxxxx
- Delivery-date: Sun, 06 Oct 2024 08:06:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Sun, Oct 6, 2024 at 2:00 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Sat, 5 Oct 2024 at 16:37, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> >
> > Sadly, that is not correct; neither gcc nor clang uses lea:
>
> Looking around, this may be intentional. At least according to Agner,
> several cores do better at "mov immediate" compared to "lea".
>
> Eg a RIP-relative LEA on Zen 2 gets a throughput of two per cycle, but
> a "MOV r,i" gets four. That got fixed in Zen 3 and later, but
> apparently Intel had similar issues (Ivy Bridge: 1 LEA per cycle, vs 3
> "mov i,r". Haswell is 1:4).
Yes, this is the case. I just missed your reply when replying to
Peter's mail with a not so precise answer.
Uros.
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