Re: [PATCH v2 0/3] RISC-V: ifunced memcpy using new kernel hwprobe interface

[Palmer Dabbelt <palmer@rivosinc.com>]

On Tue, 28 Mar 2023 16:41:10 PDT (-0700), adhemerval.zanella@linaro.org wrote:
>
>
> On 28/03/23 19:54, Palmer Dabbelt wrote:
>> On Tue, 21 Feb 2023 11:15:34 PST (-0800), Evan Green wrote:
>>>
>>> This series illustrates the use of a proposed Linux syscall that
>>> enumerates architectural information about the RISC-V cores the system
>>> is running on. In this series we expose a small wrapper function around
>>> the syscall. An ifunc selector for memcpy queries it to see if unaligned
>>> access is "fast" on this hardware. If it is, it selects a newly provided
>>> implementation of memcpy that doesn't work hard at aligning the src and
>>> destination buffers.
>>>
>>> This is somewhat of a proof of concept for the syscall itself, but I do
>>> find that in my goofy memcpy test [1], the unaligned memcpy performed at
>>> least as well as the generic C version. This is however on Qemu on an M1
>>> mac, so not a test of any real hardware (more a smoke test that the
>>> implementation isn't silly).
>>
>> QEMU isn't a good enough benchmark to justify a new memcpy routine in glibc.  Evan has a D1, which does support misaligned access and runs some simple benchmarks faster.  There's also been some minor changes to the Linux side of things that warrant a v3 anyway, so he'll just post some benchmarks on HW along with that.
>>
>> Aside from those comments,
>>
>> Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
>>
>> There's a lot more stuff to probe for, but I think we've got enough of a proof of concept for the hwprobe stuff that we can move forward with the core interface bits in Linux/glibc and then unleash the chaos...
>>
>> Unless anyone else has comments?
>
> Until riscv_hwprobe is not on Linus tree as official Linux ABI this patchset
> can not be installed.  We failed to enforce it on some occasion (like Intel
> CET) and it turned out a complete mess after some years...

Sorry if that wasn't clear, I was asking if there were any more comments 
from the glibc side of things before merging the Linux code.