[PATCH v2 2/2] RISC-V: hwprobe: Add SCALAR to misaligned perf defines

[Conor Dooley]

On Tue, Jun 25, 2024 at 12:08:09PM -0700, Evan Green wrote:
> On Tue, Jun 25, 2024 at 11:35 AM Conor Dooley <conor at kernel.org> wrote:
> >
> > On Tue, Jun 25, 2024 at 09:51:21AM -0700, Evan Green wrote:
> > > In preparation for misaligned vector performance hwprobe keys, rename
> > > the hwprobe key values associated with misaligned scalar accesses to
> > > include the term SCALAR.
> > >
> > > Signed-off-by: Evan Green <evan at rivosinc.com>
> > >
> > > ---
> > >
> > > Changes in v2:
> > >  - Added patch to rename misaligned perf key values (Palmer)
> > >
> > >  Documentation/arch/riscv/hwprobe.rst       | 20 ++++++++++----------
> > >  arch/riscv/include/uapi/asm/hwprobe.h      | 10 +++++-----
> > >  arch/riscv/kernel/sys_hwprobe.c            | 10 +++++-----
> > >  arch/riscv/kernel/traps_misaligned.c       |  6 +++---
> > >  arch/riscv/kernel/unaligned_access_speed.c | 12 ++++++------
> > >  5 files changed, 29 insertions(+), 29 deletions(-)
> > >
> > > diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> > > index c9f570b1ab60..83f7f3c1347f 100644
> > > --- a/Documentation/arch/riscv/hwprobe.rst
> > > +++ b/Documentation/arch/riscv/hwprobe.rst
> > > @@ -215,22 +215,22 @@ The following keys are defined:
> > >    the performance of misaligned scalar word accesses on the selected set of
> > >    processors.
> > >
> > > -  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNKNOWN`: The performance of misaligned
> > > -    accesses is unknown.
> > > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SCALAR_UNKNOWN`: The performance of
> > > +    misaligned accesses is unknown.
> > >
> > > -  * :c:macro:`RISCV_HWPROBE_MISALIGNED_EMULATED`: Misaligned accesses are
> > > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SCALAR_EMULATED`: Misaligned accesses are
> > >      emulated via software, either in or below the kernel.  These accesses are
> > >      always extremely slow.
> > >
> > > -  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SLOW`: Misaligned word accesses are
> > > -    slower than equivalent byte accesses.  Misaligned accesses may be supported
> > > -    directly in hardware, or trapped and emulated by software.
> > > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SCALAR_SLOW`: Misaligned word accesses
> > > +    are slower than equivalent byte accesses.  Misaligned accesses may be
> > > +    supported directly in hardware, or trapped and emulated by software.
> > >
> > > -  * :c:macro:`RISCV_HWPROBE_MISALIGNED_FAST`: Misaligned word accesses are
> > > -    faster than equivalent byte accesses.
> > > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SCALAR_FAST`: Misaligned word accesses
> > > +    are faster than equivalent byte accesses.
> > >
> > > -  * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNSUPPORTED`: Misaligned accesses are
> > > -    not supported at all and will generate a misaligned address fault.
> > > +  * :c:macro:`RISCV_HWPROBE_MISALIGNED_SCALAR_UNSUPPORTED`: Misaligned accesses
> > > +    are not supported at all and will generate a misaligned address fault.
> > >
> > >  * :c:macro:`RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE`: An unsigned int which
> > >    represents the size of the Zicboz block in bytes.
> > > diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> > > index 22073533cea8..e11684d8ae1c 100644
> > > --- a/arch/riscv/include/uapi/asm/hwprobe.h
> > > +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> > > @@ -66,11 +66,11 @@ struct riscv_hwprobe {
> > >  #define              RISCV_HWPROBE_EXT_ZVE64F        (1ULL << 40)
> > >  #define              RISCV_HWPROBE_EXT_ZVE64D        (1ULL << 41)
> > >  #define RISCV_HWPROBE_KEY_CPUPERF_0  5
> > > -#define              RISCV_HWPROBE_MISALIGNED_UNKNOWN        0
> > > -#define              RISCV_HWPROBE_MISALIGNED_EMULATED       1
> > > -#define              RISCV_HWPROBE_MISALIGNED_SLOW           2
> > > -#define              RISCV_HWPROBE_MISALIGNED_FAST           3
> > > -#define              RISCV_HWPROBE_MISALIGNED_UNSUPPORTED    4
> > > +#define              RISCV_HWPROBE_MISALIGNED_SCALAR_UNKNOWN         0
> > > +#define              RISCV_HWPROBE_MISALIGNED_SCALAR_EMULATED        1
> > > +#define              RISCV_HWPROBE_MISALIGNED_SCALAR_SLOW            2
> > > +#define              RISCV_HWPROBE_MISALIGNED_SCALAR_FAST            3
> > > +#define              RISCV_HWPROBE_MISALIGNED_SCALAR_UNSUPPORTED     4
> > >  #define              RISCV_HWPROBE_MISALIGNED_MASK           7
> >
> > How come the "old" names do not need to be preserved for userspace?
> 
> It depends on what exactly the big userspace compatibility rule is.
> This preserves binary compatibility, which I think is the big one, but
> breaks source compatibility, though with an easy translation to fix.
> We could keep the old names around, but then it seems sort of silly to
> introduce the new names. I introduced this patch upon request, so I
> don't personally have a horse in the race on this one.

So apparently this isn't quite Palmer actually wanted. In today's call
he suggested that he'd send a new version himself, but also that what we
should do define a new key for scalar /and/ new add new defines values that
contain the word scalar, retaining the old defines. The values can of
course be the same.
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