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Date: Wed, 19 Apr 2023 13:33:08 +0800 (GMT+08:00)
From: 张飞 <zhangfei@...iscas.ac.cn>
To: musl@...ts.openwall.com
Subject: Re: Re: memset_riscv64
Hi！
I have revised the implementation of memset, which includes two versions of the basic instruction set and
vector instruction implementation, and used macro definitions to determine whether riscv hardware
supports vector extension.
The reason for implementing two versions is to hope that the memset implemented
using the basic instruction set can be applicable to all RISCV architecture CPUs, and the vector version can
accelerate the hardware supporting vector expansion.
At present, the riscv vector extension instruction set is in a frozen state, and the instruction set is stable.
In other open source libraries, such as openssl and openCV, riscv vector optimization is available.
I conducted tests on different data volumes and compared the performance of memset functions implemented
in C language, basic instruction set, and vector instruction set.The test case is test_memset.c
Performance comparison between C language implementation and assembly implementation was tested on
Sifive chips(RISC-V SiFive U74 Dual Core 64 Bit RV64GC ISA Chip Platform).
The test results are as follows.when it is less than 16 bytes, the performance of C language implementation is
better; From 16 bytes to 32768 bytes, the basic instruction implementation performance is better, with an average
improvement of over 30%; When it is greater than 32768 bytes, the performance of both is equivalent.
--------------------------------------------------------------------------------
length(byte) C language implementation(s) Basic instruction implementation(s)
--------------------------------------------------------------------------------
4 0.00000352 0.000004001
8 0.000004001 0.000005441
16 0.000006241 0.00000464
32 0.00000752 0.00000448
64 0.000008481 0.000005281
128 0.000009281 0.000005921
256 0.000011201 0.000007041
512 0.000014402 0.000010401
1024 0.000022563 0.000016962
2048 0.000039205 0.000030724
4096 0.000072809 0.000057768
8192 0.000153459 0.000132793
16384 0.000297157 0.000244992
32768 0.000784416 0.000735298
65536 0.005005252 0.004987382
131072 0.011286821 0.011256855
262144 0.023295169 0.022932165
524288 0.04647724 0.046084839
1048576 0.094114058 0.0932383
--------------------------------------------------------------------------------
Due to the lack of a chip that supports vector extension, I conducted a performance comparison test of memset
using C language and vector implementation on the Spike simulator, which has certain reference value.
It can be clearly seen that vector implementation is more efficient than C language implementation,
with an average performance improvement of over 200%.
--------------------------------------------------------------------------------
length(byte) C language implementation(s) Vector instruction implementation(s)
--------------------------------------------------------------------------------
4 0.000002839 0.000002939
8 0.000003239 0.000002939
16 0.000005239 0.000002939
32 0.000007039 0.000002939
64 0.000008039 0.000002939
128 0.000009239 0.000002939
256 0.000011639 0.000003539
512 0.000016439 0.000004739
1024 0.000026039 0.000007139
2048 0.000045239 0.000011939
4096 0.000083639 0.000021539
8192 0.000162298 0.000042598
16384 0.000317757 0.000082857
32768 0.000628675 0.000163375
65536 0.001250511 0.000324411
131072 0.002494183 0.000646483
262144 0.004981527 0.001290627
524288 0.009956215 0.002578915
1048576 0.019905591 0.005155491
--------------------------------------------------------------------------------
So I hope that a more efficient assembly implementation of riscv64 memset functions can be
integrated into musl and compatible with different riscv architectures' CPUs.
Fei Zhang
> -----原始邮件-----
> 发件人: "Pedro Falcato" <pedro.falcato@...il.com>
> 发送时间: 2023-04-11 17:48:31 (星期二)
> 收件人: musl@...ts.openwall.com
> 抄送:
> 主题: Re: [musl] memset_riscv64
>
> On Tue, Apr 11, 2023 at 3:18 AM 张飞 <zhangfei@...iscas.ac.cn> wrote:
> >
> > Hello,
> >
> > Currently, there is no assembly implementation of the memset function for riscv64 in Musl.
> > This patch is a riscv64 assembly implementation of the memset function, which is implemented using the basic instruction set and
> > has better performance than the c language implementation in Musl. I hope it can be integrated into Musl.
>
> Hi!
>
> Do you have performance measurements here? What exactly is the difference?
> As far as I know, no one is actively optimizing on riscv yet, only
> some movements in the upstream kernel (to prepare for vector extension
> stuff, unaligned loads/stores) and the corresponding glibc patches.
> Mainly because it's still super unobtanium and in very early stages,
> so optimizing is very hard.
>
> So what hardware did you use? Is there a large gain here? Given that
> your memset looks so simple, wouldn't it just be easier to write this
> in C?
>
> --
> Pedro
</zhangfei@...iscas.ac.cn></pedro.falcato@...il.com>
Download attachment "memset_riscv64.patch" of type "application/octet-stream" (2646 bytes)
View attachment "test_memset.c" of type "text/plain" (929 bytes)
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