From 61caf7cce90d77840a67353db78cea146c2c8f7b Mon Sep 17 00:00:00 2001 From: hujun5 Date: Thu, 11 Jan 2024 21:34:24 +0800 Subject: [PATCH] types: on some arch, execution speed can be accelerated in arm64 Let's see how the following code looks like in assembly volatile cpu_set_t g_cpu_set; cpu_set_t set_cpu_set_t_set(int cpu) { g_cpu_set &= ~(1 << cpu); return g_cpu_set; } when typedef volatile uint32_t cpu_set_t; Dump of assembler code for function set_cpu_set_t_set: 0x0000000040288570 <+0>: adrp x2, 0x403ce000 0x0000000040288574 <+4>: ldr w3, [x2, #2368] 0x0000000040288578 <+8>: mov w1, #0x1 0x000000004028857c <+12>: lsl w1, w1, w0 0x0000000040288580 <+16>: bic w1, w3, w1 0x0000000040288584 <+20>: str w1, [x2, #2368] 0x0000000040288588 <+24>: ldr w0, [x2, #2368] 0x000000004028858c <+28>: ret when typedef volatile uint8_t cpu_set_t; Dump of assembler code for function set_cpu_set_t_set: 0x000000004028856c <+0>: adrp x2, 0x403ce000 0x0000000040288570 <+4>: ldrb w3, [x2, #2336] 0x0000000040288574 <+8>: mov w1, #0x1 0x0000000040288578 <+12>: and w3, w3, #0xff // At this time, there will be one more instruction 0x000000004028857c <+16>: lsl w1, w1, w0 0x0000000040288580 <+20>: bic w1, w3, w1 0x0000000040288584 <+24>: strb w1, [x2, #2336] 0x0000000040288588 <+28>: ldrb w0, [x2, #2336] 0x000000004028858c <+32>: ret test: We can use qemu for testing. compiling make distclean -j20; ./tools/configure.sh -l qemu-armv8a:nsh_smp ;make -j20 running qemu-system-aarch64 -cpu cortex-a53 -smp 4 -nographic -machine virt,virtualization=on,gic-version=3 -net none -chardev stdio,id=con,mux=on -serial chardev:con -mon chardev=con,mode=readline -kernel ./nuttx Signed-off-by: hujun5 --- include/sys/types.h | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/include/sys/types.h b/include/sys/types.h index d19448d0d2..a87827b5f1 100644 --- a/include/sys/types.h +++ b/include/sys/types.h @@ -268,11 +268,7 @@ typedef int32_t suseconds_t; /* This is the smallest integer type that will hold a bitset of all CPUs */ -#if (CONFIG_SMP_NCPUS <= 8) -typedef volatile uint8_t cpu_set_t; -#elif (CONFIG_SMP_NCPUS <= 16) -typedef volatile uint16_t cpu_set_t; -#elif (CONFIG_SMP_NCPUS <= 32) +#if (CONFIG_SMP_NCPUS <= 32) typedef volatile uint32_t cpu_set_t; #else # error SMP: Extensions needed to support this number of CPUs