Re: [PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND_RET for all syscalls
From: Tiezhu Yang
Date: Wed Jun 22 2022 - 20:43:47 EST
Cc Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
On 06/22/2022 06:01 PM, Huacai Chen wrote:
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.
There is another way to look at what is going on.
This patch is related with syscall, I prefer to
observe "System Call Overhead" in the test results.
Here are the INDEX of "System Call Overhead" in your test results:
thread before_patch after_patch gain
single 371.6 375.7 1.103%
multi 1353.0 1366.5 0.998%
For now, I would like to wait for other people's review.
If the conclusion is the optimization is meaningless,
I am fine with ignoring this patch.
Thanks,
Tiezhu
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