Re: [PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND_RET for all syscalls

From: Huacai Chen
Date: Wed Jun 22 2022 - 06:02:20 EST

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Hi, Tiezhu,

On Tue, Jun 21, 2022 at 6:08 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
>
> In handle_syscall, it is unnecessary to call RESTORE_ALL_AND_RET
> for all syscalls.
>
> (1) rt_sigreturn call RESTORE_ALL_AND_RET.
> (2) The other syscalls call RESTORE_STATIC_SOME_SP_AND_RET.
>
> This patch only adds the minimal changes as simple as possible
> to reduce the code complexity, at the same time, it can reduce
> many load instructions.
>
> Here are the test environments:
>
> Hardware: Loongson-LS3A5000-7A1000-1w-A2101
> Firmware: UDK2018-LoongArch-A2101-pre-beta8 [1]
> System: loongarch64-clfs-system-5.0 [2]
>
> The system passed functional testing used with the following
> test case without and with this patch:
>
> git clone https://github.com/hevz/sigaction-test.git
> cd sigaction-test
> make check
>
> Additionally, use UnixBench syscall to test the performance:
>
> git clone https://github.com/kdlucas/byte-unixbench.git
> cd byte-unixbench/UnixBench/
> make
> pgms/syscall 600
>
> In order to avoid the performance impact, add init=/bin/bash
> to the boot cmdline.
>
> Here is the test result, the bigger the better, it shows about
> 1.2% gain tested with close, getpid and exec [3]:
>
> duration without_this_patch with_this_patch
> 600 s 626558267 lps 634244079 lps
>
> [1] https://github.com/loongson/Firmware/tree/main/5000Series/PC/A2101
> [2] https://github.com/sunhaiyong1978/CLFS-for-LoongArch/releases/tag/5.0
> [3] https://github.com/kdlucas/byte-unixbench/blob/master/UnixBench/src/syscall.c
I test your patch and the whole UnixBench result is like this:

Before patch, single thread:

System Benchmarks Index Values BASELINE RESULT INDEX
Dhrystone 2 using register variables 116700.0 9235787.7 791.4
Double-Precision Whetstone 55.0 2758.7 501.6
Execl Throughput 43.0 2386.8 555.1
File Copy 1024 bufsize 2000 maxblocks 3960.0 191752.0 484.2
File Copy 256 bufsize 500 maxblocks 1655.0 78737.9 475.8
File Copy 4096 bufsize 8000 maxblocks 5800.0 297402.5 512.8
Pipe Throughput 12440.0 353658.1 284.3
Pipe-based Context Switching 4000.0 120140.8 300.4
Process Creation 126.0 5735.0 455.2
Shell Scripts (1 concurrent) 42.4 2701.5 637.1
Shell Scripts (8 concurrent) 6.0 894.9 1491.5
System Call Overhead 15000.0 557467.4 371.6
========
System Benchmarks Index Score 516.1

After patch, single thread:

System Benchmarks Index Values BASELINE RESULT INDEX
Dhrystone 2 using register variables 116700.0 9235688.9 791.4
Double-Precision Whetstone 55.0 2758.7 501.6
Execl Throughput 43.0 2377.8 553.0
File Copy 1024 bufsize 2000 maxblocks 3960.0 192545.5 486.2
File Copy 256 bufsize 500 maxblocks 1655.0 79735.0 481.8
File Copy 4096 bufsize 8000 maxblocks 5800.0 299621.9 516.6
Pipe Throughput 12440.0 354969.1 285.3
Pipe-based Context Switching 4000.0 118307.5 295.8
Process Creation 126.0 5757.0 456.9
Shell Scripts (1 concurrent) 42.4 2695.4 635.7
Shell Scripts (8 concurrent) 6.0 894.4 1490.6
System Call Overhead 15000.0 563582.7 375.7
========
System Benchmarks Index Score 517.0

Before patch, multi-threads:

System Benchmarks Index Values BASELINE RESULT INDEX
Dhrystone 2 using register variables 116700.0 36943633.4 3165.7
Double-Precision Whetstone 55.0 11035.8 2006.5
Execl Throughput 43.0 8800.1 2046.5
File Copy 1024 bufsize 2000 maxblocks 3960.0 277638.3 701.1
File Copy 256 bufsize 500 maxblocks 1655.0 92530.5 559.1
File Copy 4096 bufsize 8000 maxblocks 5800.0 524344.3 904.0
Pipe Throughput 12440.0 1359237.2 1092.6
Pipe-based Context Switching 4000.0 571511.4 1428.8
Process Creation 126.0 20823.3 1652.6
Shell Scripts (1 concurrent) 42.4 6883.9 1623.6
Shell Scripts (8 concurrent) 6.0 981.7 1636.1
System Call Overhead 15000.0 2029539.8 1353.0
========
System Benchmarks Index Score 1367.4

After patch, multi-threads:

System Benchmarks Index Values BASELINE RESULT INDEX
Dhrystone 2 using register variables 116700.0 36943793.6 3165.7
Double-Precision Whetstone 55.0 11035.5 2006.4
Execl Throughput 43.0 8768.3 2039.1
File Copy 1024 bufsize 2000 maxblocks 3960.0 277962.9 701.9
File Copy 256 bufsize 500 maxblocks 1655.0 92059.7 556.3
File Copy 4096 bufsize 8000 maxblocks 5800.0 525937.5 906.8
Pipe Throughput 12440.0 1361566.6 1094.5
Pipe-based Context Switching 4000.0 575835.4 1439.6
Process Creation 126.0 20426.4 1621.1
Shell Scripts (1 concurrent) 42.4 6877.5 1622.0
Shell Scripts (8 concurrent) 6.0 980.3 1633.8
System Call Overhead 15000.0 2049771.6 1366.5
========
System Benchmarks Index Score 1366.6

>From my point of view, the benefit is negligible.

Huacai

>
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> ---
> arch/loongarch/include/asm/stackframe.h | 5 +++++
> arch/loongarch/kernel/entry.S | 15 +++++++++++++++
> 2 files changed, 20 insertions(+)
>
> diff --git a/arch/loongarch/include/asm/stackframe.h b/arch/loongarch/include/asm/stackframe.h
> index 4ca9530..551ab8f 100644
> --- a/arch/loongarch/include/asm/stackframe.h
> +++ b/arch/loongarch/include/asm/stackframe.h
> @@ -216,4 +216,9 @@
> RESTORE_SP_AND_RET \docfi
> .endm
>
> + .macro RESTORE_STATIC_SOME_SP_AND_RET docfi=0
> + RESTORE_STATIC \docfi
> + RESTORE_SOME \docfi
> + RESTORE_SP_AND_RET \docfi
> + .endm
> #endif /* _ASM_STACKFRAME_H */
> diff --git a/arch/loongarch/kernel/entry.S b/arch/loongarch/kernel/entry.S
> index d5b3dbc..c764c99 100644
> --- a/arch/loongarch/kernel/entry.S
> +++ b/arch/loongarch/kernel/entry.S
> @@ -14,6 +14,7 @@
> #include <asm/regdef.h>
> #include <asm/stackframe.h>
> #include <asm/thread_info.h>
> +#include <asm/unistd.h>
>
> .text
> .cfi_sections .debug_frame
> @@ -62,9 +63,23 @@ SYM_FUNC_START(handle_syscall)
> li.d tp, ~_THREAD_MASK
> and tp, tp, sp
>
> + /* Syscall number held in a7, we can store it in TI_SYSCALL. */
> + LONG_S a7, tp, TI_SYSCALL
> +
> move a0, sp
> bl do_syscall
>
> + /*
> + * Syscall number held in a7 which is stored in TI_SYSCALL.
> + * rt_sigreturn call RESTORE_ALL_AND_RET.
> + * The other syscalls call RESTORE_STATIC_SOME_SP_AND_RET.
> + */
> + LONG_L t3, tp, TI_SYSCALL
> + li.w t4, __NR_rt_sigreturn
> + beq t3, t4, 1f
> +
> + RESTORE_STATIC_SOME_SP_AND_RET
> +1:
> RESTORE_ALL_AND_RET
> SYM_FUNC_END(handle_syscall)
>
> --
> 2.1.0
>

Next message: Eric Dumazet: "Re: [PATCH net] net: ensure all external references are released in deferred skbuffs"
Previous message: cy_huang: "[PATCH v2 4/4] input: misc: rt5120: Add power key support"
In reply to: Tiezhu Yang: "[PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND_RET for all syscalls"
Next in thread: Tiezhu Yang: "Re: [PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND_RET for all syscalls"
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