linux-kernel - Re: [PATCH v9 0/6] RISC-V: Detect and report speed of unaligned vector accesses

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Message-ID: <Zu3qAdGYJfNPTK15@ghost>
Date: Fri, 20 Sep 2024 23:32:49 +0200
From: Charlie Jenkins <charlie@...osinc.com>
To: Palmer Dabbelt <palmer@...belt.com>
Cc: jesse@...osinc.com, linux-riscv@...ts.infradead.org, corbet@....net,
	Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
	Conor Dooley <conor@...nel.org>, robh@...nel.org,
	krzk+dt@...nel.org, cleger@...osinc.com,
	Evan Green <evan@...osinc.com>, ajones@...tanamicro.com,
	xiao.w.wang@...el.com, andy.chiu@...ive.com, ebiggers@...gle.com,
	greentime.hu@...ive.com, Bjorn Topel <bjorn@...osinc.com>,
	Heiko Stuebner <heiko@...ech.de>, costa.shul@...hat.com,
	akpm@...ux-foundation.org, bhe@...hat.com, apatel@...tanamicro.com,
	zong.li@...ive.com, samitolvanen@...gle.com,
	ben.dooks@...ethink.co.uk, alexghiti@...osinc.com,
	gustavoars@...nel.org, erick.archer@....com, j.granados@...sung.com,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v9 0/6] RISC-V: Detect and report speed of unaligned
 vector accesses

On Fri, Sep 20, 2024 at 11:01:10PM +0200, Charlie Jenkins wrote:
> On Fri, Sep 20, 2024 at 05:57:22AM -0700, Palmer Dabbelt wrote:
> > On Tue, 20 Aug 2024 08:24:18 PDT (-0700), jesse@...osinc.com wrote:
> > > Adds support for detecting and reporting the speed of unaligned vector
> > > accesses on RISC-V CPUs. Adds vec_misaligned_speed key to the hwprobe
> > > adds Zicclsm to cpufeature and fixes the check for scalar unaligned
> > > emulated all CPUs. The vec_misaligned_speed key keeps the same format
> > > as the scalar unaligned access speed key.
> > > 
> > > This set does not emulate unaligned vector accesses on CPUs that do not
> > > support them. Only reports if userspace can run them and speed of
> > > unaligned vector accesses if supported.
> > > 
> > > The Zicclsm is patches are no longer related to this set.
> > > 
> > > Changes in v6:
> > >  Added ("RISC-V: Scalar unaligned access emulated on hotplug CPUs")
> > > 
> > > Changes in V8:
> > >  Dropped Zicclsm
> > >  s/RISCV_HWPROBE_VECTOR_MISALIGNED/RISCV_HWPROBE_MISALIGNED_VECTOR/g
> > >   to match RISCV_HWPROBE_MISALIGNED_SCALAR_*
> > >  Rebased onto palmer/fixes (32d5f7add080a936e28ab4142bfeea6b06999789)
> > > 
> > > Changes in V9:
> > >  Missed a RISCV_HWPROBE_VECTOR_MISALIGNED...
> > > 
> > > Jesse Taube (6):
> > >   RISC-V: Check scalar unaligned access on all CPUs
> > >   RISC-V: Scalar unaligned access emulated on hotplug CPUs
> > >   RISC-V: Replace RISCV_MISALIGNED with RISCV_SCALAR_MISALIGNED
> > >   RISC-V: Detect unaligned vector accesses supported
> > >   RISC-V: Report vector unaligned access speed hwprobe
> > >   RISC-V: hwprobe: Document unaligned vector perf key
> > > 
> > >  Documentation/arch/riscv/hwprobe.rst       |  16 +++
> > >  arch/riscv/Kconfig                         |  57 +++++++-
> > >  arch/riscv/include/asm/cpufeature.h        |  10 +-
> > >  arch/riscv/include/asm/entry-common.h      |  11 --
> > >  arch/riscv/include/asm/hwprobe.h           |   2 +-
> > >  arch/riscv/include/asm/vector.h            |   2 +
> > >  arch/riscv/include/uapi/asm/hwprobe.h      |   5 +
> > >  arch/riscv/kernel/Makefile                 |   3 +-
> > >  arch/riscv/kernel/copy-unaligned.h         |   5 +
> > >  arch/riscv/kernel/fpu.S                    |   4 +-
> > >  arch/riscv/kernel/sys_hwprobe.c            |  41 ++++++
> > >  arch/riscv/kernel/traps_misaligned.c       | 131 +++++++++++++++--
> > >  arch/riscv/kernel/unaligned_access_speed.c | 156 +++++++++++++++++++--
> > >  arch/riscv/kernel/vec-copy-unaligned.S     |  58 ++++++++
> > >  arch/riscv/kernel/vector.c                 |   2 +-
> > >  15 files changed, 465 insertions(+), 38 deletions(-)
> > >  create mode 100644 arch/riscv/kernel/vec-copy-unaligned.S
> > > 
> > > base-commit: 32d5f7add080a936e28ab4142bfeea6b06999789
> > 
> > I get a
> > 
> > arch/riscv/kernel/traps_smisaligned.c: In function 'check_vector_unaligned_access_emulated':
> > arch/riscv/kernel/traps_misaligned.c:591:9: error: unknown register name 'v0' in 'asm'
> >  591 |         __asm__ __volatile__ (
> >      |         ^~~~~~~
> > 
> > on rv32/defconfig.  Looks like just a missing Kconfg guard as this depends
> > on V support in the toolchain.
> 
> There was an interesting iteraction here!
> RISCV_PROBE_VECTOR_UNALIGNED_ACCESS was selecting
> RISCV_VECTOR_MISALIGNED but that bypasses the depends on check of
> RISCV_ISA_V. I'll send an update for Jesse with the fix for that one
> patch.

I take it back, I am not able to reproduce this.
RISCV_PROBE_VECTOR_UNALIGNED_ACCESS is hidden behind "Vector unaligned
Accesses Support" which depends on RISCV_ISA_V. This function that is
erroring has the code:

#ifdef CONFIG_RISCV_VECTOR_MISALIGNED
void check_vector_unaligned_access_emulated(struct work_struct *work __always_unused)
...

Since it is hidden behind CONFIG_RISCV_VECTOR_MISALIGNED, I am unsure
how it is possible that this error is leaking through. The error you
posted is also kind of odd because the first file you have is
"arch/riscv/kernel/traps_smisaligned.c" but the actual file is
"arch/riscv/kernel/traps_misaligned.c".

> - Charlie
>