From: Philipp Tomsich <philipp.tomsich@vrull.eu>
To: DJ Delorie <dj@redhat.com>
Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>,
christoph.muellner@vrull.eu, libc-alpha@sourceware.org,
palmer@dabbelt.com, darius@bluespec.com, andrew@sifive.com,
vineetg@rivosinc.com, kito.cheng@sifive.com,
jeffreyalaw@gmail.com, heiko.stuebner@vrull.eu
Subject: Re: [RFC PATCH 00/19] riscv: ifunc support with optimized mem*/str*/cpu_relax routines
Date: Tue, 7 Feb 2023 20:32:08 +0100 [thread overview]
Message-ID: <CAAeLtUAuSidHYBpczShEhXwYfkJeAz2MMz1kGkBkv5wY38TVhA@mail.gmail.com> (raw)
In-Reply-To: <xna61pcs63.fsf@greed.delorie.com>
On Tue, 7 Feb 2023 at 18:16, DJ Delorie <dj@redhat.com> wrote:
>
> Adhemerval Zanella Netto <adhemerval.zanella@linaro.org> writes:
> > So now we have 3 different proposal mechanism to provide implementation runtime
> > selection on riscv:
> >
> > 1. The sysdep mechanism to select optimized routines based on compiler/ABI
> > done at build time. It is the current mechanism and it is also used
> > on rvv routines [1].
> >
> > 2. A ifunc one using a new riscv syscall to query the kernel the required
> > information.
> >
> > 3. Another ifunc one using riscv specific environment variable.
>
> I'm also going to oppose #3 on principles. We've been removing the use
> of environment variables for tuning, in favor of tunables.
You may have missed the essential part of the commit message:
> > Since we don't have an interface to get this information from the
> > kernel (at the moment), this patch uses environment variables instead,
> > which is also why this patch should not be considered for upstream
> > inclusion and is explicitly tagged as RFC.
So this patch has always been a stand-in until option #2 is ready.
I am strongly opinionated towards a mechanism that uses existing
mechanisms in the ELF auxiliary vector to pass information — and tries
to avoid the introduction of a new arch-specific syscall. if possible.
> If we have a way to auto-detect the best implementation without relying
> on the user, that's my preference. Users are unreliable and require
> documentation. The compiler likely doesn't have access to the
> hardware[*], so must rely on the user. Thus, my preference is #2 - the
> kernel has access to the hardware and its device tree, and can tell the
> userspace what capabilities are available.
>
> I would not be opposed to a tunable that overrides the autodetection; we
> have something similar for x86. But the default (and should be) is
> "works basically correctly without user intervention".
>
> [*] you can run gcc on the "right" hardware, but typically we
> build-once-run-everywhere.
>
next prev parent reply other threads:[~2023-02-07 19:32 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-07 0:15 Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 01/19] Inhibit early libcalls before ifunc support is ready Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 02/19] riscv: LEAF: Use C_LABEL() to construct the asm name for a C symbol Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 03/19] riscv: Add ENTRY_ALIGN() macro Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 04/19] riscv: Add hart feature run-time detection framework Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 05/19] riscv: Introduction of ISA extensions Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 06/19] riscv: Adding ISA string parser for environment variables Christoph Muellner
2023-02-07 6:20 ` David Abdurachmanov
2023-02-07 0:16 ` [RFC PATCH 07/19] riscv: hart-features: Add fast_unaligned property Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 08/19] riscv: Add (empty) ifunc framework Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 09/19] riscv: Add ifunc support for memset Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 10/19] riscv: Add accelerated memset routines for RV64 Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 11/19] riscv: Add ifunc support for memcpy/memmove Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 12/19] riscv: Add accelerated memcpy/memmove routines for RV64 Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 13/19] riscv: Add ifunc support for strlen Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 14/19] riscv: Add accelerated strlen routine Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 15/19] riscv: Add ifunc support for strcmp Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 16/19] riscv: Add accelerated strcmp routines Christoph Muellner
2023-02-07 11:57 ` Xi Ruoyao
2023-02-07 14:15 ` Christoph Müllner
2023-03-31 5:06 ` Jeff Law
2023-03-31 12:31 ` Adhemerval Zanella Netto
2023-03-31 14:30 ` Jeff Law
2023-03-31 14:48 ` Adhemerval Zanella Netto
2023-03-31 17:19 ` Palmer Dabbelt
2023-03-31 14:32 ` Jeff Law
2023-02-07 0:16 ` [RFC PATCH 17/19] riscv: Add ifunc support for strncmp Christoph Muellner
2023-02-07 0:16 ` [RFC PATCH 18/19] riscv: Add an optimized strncmp routine Christoph Muellner
2023-02-07 1:19 ` Noah Goldstein
2023-02-08 15:13 ` Philipp Tomsich
2023-02-08 17:55 ` Palmer Dabbelt
2023-02-08 19:48 ` Adhemerval Zanella Netto
2023-02-08 18:04 ` Noah Goldstein
2023-02-07 0:16 ` [RFC PATCH 19/19] riscv: Add __riscv_cpu_relax() to allow yielding in busy loops Christoph Muellner
2023-02-07 0:23 ` Andrew Waterman
2023-02-07 0:29 ` Christoph Müllner
2023-02-07 2:59 ` [RFC PATCH 00/19] riscv: ifunc support with optimized mem*/str*/cpu_relax routines Kito Cheng
2023-02-07 16:40 ` Adhemerval Zanella Netto
2023-02-07 17:16 ` DJ Delorie
2023-02-07 19:32 ` Philipp Tomsich [this message]
2023-02-07 21:14 ` DJ Delorie
2023-02-08 11:26 ` Christoph Müllner
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