From: Nick Desaulniers <ndesaulniers@google.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
x86@kernel.org, Kostya Serebryany <kcc@google.com>,
Andrey Ryabinin <ryabinin.a.a@gmail.com>,
Andrey Konovalov <andreyknvl@gmail.com>,
Alexander Potapenko <glider@google.com>,
Taras Madan <tarasmadan@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
"H . J . Lu" <hjl.tools@gmail.com>,
Andi Kleen <ak@linux.intel.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
Bharata B Rao <bharata@amd.com>,
Jacob Pan <jacob.jun.pan@linux.intel.com>,
Ashok Raj <ashok.raj@intel.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Sami Tolvanen <samitolvanen@google.com>,
joao@overdrivepizza.com
Subject: Re: [PATCHv14 08/17] x86/mm: Reduce untagged_addr() overhead until the first LAM user
Date: Tue, 17 Jan 2023 10:26:22 -0800 [thread overview]
Message-ID: <CAKwvOdnCJmcGurUpHcdO44vVazz67jGDTXzug9LGv6C84xGmPw@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wj4HUBvCvfX3oZLZAZTzPc2vdwsObFqnOsQ-UZrdzm_rQ@mail.gmail.com>
On Tue, Jan 17, 2023 at 9:29 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Tue, Jan 17, 2023 at 9:18 AM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > The reason clang seems to generate saner code is that clang seems to
> > largely ignore the whole "__builtin_expect()", at least not to the
> > point where it tries to make the unlikely case be out-of-line.
>
> Side note: that's not something new or unusual. It's been the case
> since I started testing clang - we have several code-paths where we
> use "unlikely()" to try to get very unlikely cases to be out-of-line,
> and clang just mostly ignores it, or treats it as a very weak hint. I
> think the only way to get clang to treat it as a *strong* hint is to
> use PGO.
I'd be surprised if that were intentional or by design.
Do you guys have a bug report we could look at?
> So clang ignoring the likely() hint is probably the right thing here,
> and then the wrong thing in some other places.
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2023-01-17 18:26 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-11 12:37 [PATCHv14 00/17] Linear Address Masking enabling Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 01/17] x86/mm: Rework address range check in get_user() and put_user() Kirill A. Shutemov
2023-01-18 15:49 ` Peter Zijlstra
2023-01-18 15:59 ` Linus Torvalds
2023-01-18 16:48 ` Peter Zijlstra
2023-01-18 17:01 ` Linus Torvalds
2023-01-11 12:37 ` [PATCHv14 02/17] x86: Allow atomic MM_CONTEXT flags setting Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 03/17] x86: CPUID and CR3/CR4 flags for Linear Address Masking Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 04/17] x86/mm: Handle LAM on context switch Kirill A. Shutemov
2023-01-11 13:49 ` Linus Torvalds
2023-01-11 14:14 ` Kirill A. Shutemov
2023-01-11 14:37 ` [PATCHv14.1 " Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 05/17] mm: Introduce untagged_addr_remote() Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 06/17] x86/uaccess: Provide untagged_addr() and remove tags before address check Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 07/17] x86/mm: Provide arch_prctl() interface for LAM Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 08/17] x86/mm: Reduce untagged_addr() overhead until the first LAM user Kirill A. Shutemov
2023-01-17 13:05 ` Peter Zijlstra
2023-01-17 13:57 ` Kirill A. Shutemov
2023-01-17 15:02 ` Peter Zijlstra
2023-01-17 17:18 ` Linus Torvalds
2023-01-17 17:28 ` Linus Torvalds
2023-01-17 18:26 ` Nick Desaulniers [this message]
2023-01-17 18:33 ` Linus Torvalds
2023-01-17 19:17 ` Nick Desaulniers
2023-01-17 20:10 ` Linus Torvalds
2023-01-17 20:43 ` Linus Torvalds
2023-01-17 18:14 ` Peter Zijlstra
2023-01-17 18:21 ` Peter Zijlstra
2023-01-19 23:06 ` Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 09/17] mm: Expose untagging mask in /proc/$PID/status Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 10/17] iommu/sva: Replace pasid_valid() helper with mm_valid_pasid() Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 11/17] x86/mm/iommu/sva: Make LAM and SVA mutually exclusive Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 12/17] selftests/x86/lam: Add malloc and tag-bits test cases for linear-address masking Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 13/17] selftests/x86/lam: Add mmap and SYSCALL " Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 14/17] selftests/x86/lam: Add io_uring " Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 15/17] selftests/x86/lam: Add inherit " Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 16/17] selftests/x86/lam: Add ARCH_FORCE_TAGGED_SVA " Kirill A. Shutemov
2023-01-11 12:37 ` [PATCHv14 17/17] selftests/x86/lam: Add test cases for LAM vs thread creation Kirill A. Shutemov
2023-01-18 16:49 ` [PATCHv14 00/17] Linear Address Masking enabling Peter Zijlstra
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