[PATCH v1 4/5] RISC-V: hwprobe: Support probing of misaligned accesss performance

[Palmer Dabbelt]

On Tue, 29 Nov 2022 14:10:02 PST (-0800), heiko at sntech.de wrote:
> Am Dienstag, 29. November 2022, 22:18:18 CET schrieb Palmer Dabbelt:
>> On Tue, 29 Nov 2022 13:09:49 PST (-0800), heiko at sntech.de wrote:
>> > Am Donnerstag, 13. Oktober 2022, 18:35:50 CET schrieb Palmer Dabbelt:
>> >> This allows userspace to select various routines to use based on the
>> >> performance of misaligned access on the target hardware.
>> >>
>> >> Signed-off-by: Palmer Dabbelt <palmer at rivosinc.com>
>> >
>> > [...]
>> >
>> >> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
>> >> index cbda062de9bd..54bdcf9a5049 100644
>> >> --- a/arch/riscv/include/asm/cpufeature.h
>> >> +++ b/arch/riscv/include/asm/cpufeature.h
>> >> @@ -18,4 +18,6 @@ struct riscv_cpuinfo {
>> >>
>> >>  DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
>> >>
>> >> +DECLARE_PER_CPU(long, misaligned_access_speed);
>> >
>> > just my 2ct ... wouldn't it make sense to have struct riscv_cpuinfo
>> > as the central instance for all cpu-related stuff, so
>> > misaligned_access_speed could also be part of it?
>>
>> I remember going through this one a few times and ending up here despite
>> some cleaner-looking ways of doing it.  That way does look cleaner,
>> though, so I'll give it a shot and we'll see what happens...
>>
>> >> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
>> >> index 553d755483ed..1599e40cd170 100644
>> >> --- a/arch/riscv/kernel/cpufeature.c
>> >> +++ b/arch/riscv/kernel/cpufeature.c
>> >> @@ -222,6 +226,22 @@ void __init riscv_fill_hwcap(void)
>> >>  			bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
>> >>  		else
>> >>  			bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
>> >> +
>> >> +		/*
>> >> +		 * Check for the performance of misaligned accesses.
>> >> +		 */
>> >> +		cpu = hartid_to_cpuid_map(hartid);
>> >> +		if (cpu < 0)
>> >> +			continue;
>> >> +
>> >> +		if (of_property_read_string(node, "riscv,misaligned-access-performance", &misaligned)) {
>> >
>> > I think this wants a "!" in front :-) .
>> >
>> > of_property_read_string() returns 0 on success, so running this
>> > results in a nullptr right now.
>>
>> Thanks.  I'd not gotten around to actually running this so I bet it's
>> broken in a bunch of ways.  Did you try it out?  I was really hoping to
>> find some time to get at least the simple stuff in for this cycle, but
>> too many things keep coming up.
>
> I ran the code today, so bumped into the "!" issue.
> I'm not yet "using" it, but that will come in the next days.
>
> And no worries about that time-thingy, your series already provides
> a nice pointer for the general direction to with things, so that is helpful
> in its own right.

I'm still worried about the release, as it's the last one before the 
glibc release and we'll need hooks there too.

> I will simply report any brokeness I find when it happens ;-) .

Awesome, thanks!

>
>
> Heiko