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68571a63f2
The pointer to thread_info is always available in the $tp register, so
the call to bpf_get_smp_processor_id() can be inlined into a single load
instruction.
(1) Here is the sample test.c:
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
SEC("raw_tp/sys_enter")
int test_cpuid(void *ctx)
{
return bpf_get_smp_processor_id();
}
char _license[] SEC("license") = "GPL";
(2) Here are the test steps:
sudo yum install libbpf-devel kernel-devel bpftool
clang -target bpf -O2 -c test.c -o test.o
sudo sysctl -w net.core.bpf_jit_enable=1
sudo bpftool prog show name test_cpuid
sudo rm -f /sys/fs/bpf/test_cpuid
sudo bpftool prog load test.o /sys/fs/bpf/test_cpuid
ID=$(sudo bpftool prog show pinned /sys/fs/bpf/test_cpuid | grep -oE '^[0-9]+')
sudo bpftool prog dump jited id $ID
(3) Here are the test results:
Before: 6 instructions
...
64: lu12i.w $t1, 1213
68: ori $t1, $t1, 1680
6c: lu32i.d $t1, 0
70: lu52i.d $t1, $t1, -1792
74: jirl $ra, $t1, 0
78: move $a5, $a0
...
After: 1 instruction
...
64: ld.wu $a5, $tp, 16
...
This is similar with commit 2ddec2c80b ("riscv, bpf: inline
bpf_get_smp_processor_id()").
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>