Currently, riscv linux requires at least IMA, so all platforms have a
multiplier. And I assume the 'mul' efficiency is comparable or better
than a sequence of five or so register-dependent arithmetic
instructions. Select ARCH_HAS_FAST_MULTIPLIER to get slightly nicer
codegen. Refer to commit f9b4192923fa ("[PATCH] bitops: hweight()
speedup") for more details.
In a simple benchmark test calling hweight64() in a loop, it got:
about 14% performance improvement on JH7110, tested on Milkv Mars.
about 23% performance improvement on TH1520 and SG2042, tested on
Sipeed LPI4A and SG2042 platform.
a slight performance drop on CV1800B, tested on milkv duo. Among all
riscv platforms in my hands, this is the only one which sees a slight
performance drop. It means the 'mul' isn't quick enough. However, the
situation exists on x86 too, for example, P4 doesn't have fast
integer multiplies as said in the above commit, x86 also selects
ARCH_HAS_FAST_MULTIPLIER. So let's select ARCH_HAS_FAST_MULTIPLIER
which can benefit almost riscv platforms.
Samuel also provided some performance numbers:
On Unmatched: 20% speedup for __sw_hweight32 and 30% speedup for
__sw_hweight64.
On D1: 8% speedup for __sw_hweight32 and 8% slowdown for
__sw_hweight64.
Signed-off-by: Jisheng Zhang <[email protected]>
Reviewed-by: Samuel Holland <[email protected]>
Tested-by: Samuel Holland <[email protected]>
Reviewed-by: Alexandre Ghiti <[email protected]>
---
arch/riscv/Kconfig | 1 +
1 file changed, 1 insertion(+)
Hi Palmer,
Similar as the pgprot_nx patch, this patch missed two merge window too.
Feel free to ask me questions if there's something need to be done from
my side.
Thanks
since v2:
- rebase on v6.8-rc1
- collect Reviewed-by and Tested-by tag
since v1:
- fix typo in commit msg
- add some performance numbers provided by Samuel
- collect Reviewed-by and Tested-by tag
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index be09c8836d56..aba42b2bf660 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -23,6 +23,7 @@ config RISCV
select ARCH_HAS_DEBUG_VIRTUAL if MMU
select ARCH_HAS_DEBUG_VM_PGTABLE
select ARCH_HAS_DEBUG_WX
+ select ARCH_HAS_FAST_MULTIPLIER
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_GIGANTIC_PAGE
--
2.43.0
On Mon, 25 Mar 2024 03:58:23 PDT (-0700), [email protected] wrote:
> Currently, riscv linux requires at least IMA, so all platforms have a
> multiplier. And I assume the 'mul' efficiency is comparable or better
> than a sequence of five or so register-dependent arithmetic
> instructions. Select ARCH_HAS_FAST_MULTIPLIER to get slightly nicer
> codegen. Refer to commit f9b4192923fa ("[PATCH] bitops: hweight()
> speedup") for more details.
>
> In a simple benchmark test calling hweight64() in a loop, it got:
> about 14% performance improvement on JH7110, tested on Milkv Mars.
>
> about 23% performance improvement on TH1520 and SG2042, tested on
> Sipeed LPI4A and SG2042 platform.
>
> a slight performance drop on CV1800B, tested on milkv duo. Among all
> riscv platforms in my hands, this is the only one which sees a slight
> performance drop. It means the 'mul' isn't quick enough. However, the
> situation exists on x86 too, for example, P4 doesn't have fast
> integer multiplies as said in the above commit, x86 also selects
> ARCH_HAS_FAST_MULTIPLIER. So let's select ARCH_HAS_FAST_MULTIPLIER
> which can benefit almost riscv platforms.
>
> Samuel also provided some performance numbers:
> On Unmatched: 20% speedup for __sw_hweight32 and 30% speedup for
> __sw_hweight64.
> On D1: 8% speedup for __sw_hweight32 and 8% slowdown for
> __sw_hweight64.
>
> Signed-off-by: Jisheng Zhang <[email protected]>
> Reviewed-by: Samuel Holland <[email protected]>
> Tested-by: Samuel Holland <[email protected]>
> Reviewed-by: Alexandre Ghiti <[email protected]>
> ---
> arch/riscv/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> Hi Palmer,
>
> Similar as the pgprot_nx patch, this patch missed two merge window too.
> Feel free to ask me questions if there's something need to be done from
> my side.
Sorry I missed these. I know they look small and simple, but they're
the sort of patches that have wide-reaching implications and thus just
take a long time to review for a tiny diff. I think they just got lost
in the shuffle, luckily Alex and Andrea picked up some reviews which
helps a ton.
Really the best thing to do if you stuff merged is to go review patches
that are in front of you in the patchwork queue, as that's what blocks
things from getting merged. I know that's not the most fun of
answers...
I picked these up for the tester, the code is pretty simple so hopefully
everything's OK and they'll show up on for-next proper within a day.
>
> Thanks
>
> since v2:
> - rebase on v6.8-rc1
> - collect Reviewed-by and Tested-by tag
>
> since v1:
> - fix typo in commit msg
> - add some performance numbers provided by Samuel
> - collect Reviewed-by and Tested-by tag
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index be09c8836d56..aba42b2bf660 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -23,6 +23,7 @@ config RISCV
> select ARCH_HAS_DEBUG_VIRTUAL if MMU
> select ARCH_HAS_DEBUG_VM_PGTABLE
> select ARCH_HAS_DEBUG_WX
> + select ARCH_HAS_FAST_MULTIPLIER
> select ARCH_HAS_FORTIFY_SOURCE
> select ARCH_HAS_GCOV_PROFILE_ALL
> select ARCH_HAS_GIGANTIC_PAGE
Hello:
This patch was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <[email protected]>:
On Mon, 25 Mar 2024 18:58:23 +0800 you wrote:
> Currently, riscv linux requires at least IMA, so all platforms have a
> multiplier. And I assume the 'mul' efficiency is comparable or better
> than a sequence of five or so register-dependent arithmetic
> instructions. Select ARCH_HAS_FAST_MULTIPLIER to get slightly nicer
> codegen. Refer to commit f9b4192923fa ("[PATCH] bitops: hweight()
> speedup") for more details.
>
> [...]
Here is the summary with links:
- [v3,RESEND] riscv: select ARCH_HAS_FAST_MULTIPLIER
https://git.kernel.org/riscv/c/0a16a1728790
You are awesome, thank you!
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