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

[Tiezhu Yang]

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

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