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]>
---
since v1:
- fix typo in commit msg
- add some performance numbers provided by Samuel
- collect Reviewed-by and Tested-by tag
arch/riscv/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 95a2a06acc6a..e4834fa76417 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
--
2.42.0
On Sat, Dec 02, 2023 at 09:52:02PM +0800, Jisheng Zhang 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]>
Hi @Palmer,
I saw this simple patch is missed in your for-next tree, could you
please pick it up?
Thanks in advance
> ---
>
> since v1:
> - fix typo in commit msg
> - add some performance numbers provided by Samuel
> - collect Reviewed-by and Tested-by tag
>
> arch/riscv/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 95a2a06acc6a..e4834fa76417 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
> --
> 2.42.0
>
>
> _______________________________________________
> linux-riscv mailing list
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-riscv
Hi Jisheng,
On 02/12/2023 14:52, Jisheng Zhang 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]>
> ---
>
> since v1:
> - fix typo in commit msg
> - add some performance numbers provided by Samuel
> - collect Reviewed-by and Tested-by tag
>
> arch/riscv/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 95a2a06acc6a..e4834fa76417 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
You can add:
Reviewed-by: Alexandre Ghiti <[email protected]>
Thanks,
Alex