| Message ID | 1612496049-32507-1-git-send-email-wanghongzhe@huawei.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] seccomp: Improve performace by optimizing rmb() | expand |
On Fri, 5 Feb 2021 11:34:09 +0800, wanghongzhe wrote: > According to kees's suggest, we started with the patch that just replaces > rmb() with smp_rmb() and did a performace test with UnixBench. The results > showed the overhead about 2.53% in rmb() test compared to the smp_rmb() > one, in a x86-64 kernel with CONFIG_SMP enabled running inside a qemu-kvm > vm. The test is a "syscall" testcase in UnixBench, which executes 5 > syscalls in a loop during a certain timeout (100 second in our test) and > counts the total number of executions of this 5-syscall sequence. We set a > seccomp filter with all allow rule for all used syscalls in this test > (which will go bitmap path) to make sure the rmb() will be executed. The > details for the test: > > [...] Applied to for-next/seccomp, thanks! [1/1] seccomp: Improve performace by optimizing rmb() https://git.kernel.org/kees/c/a381b70a1cf8 -- Kees Cook
diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 952dc1c90229..8505b438a590 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -1164,7 +1164,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd, * Make sure that any changes to mode from another thread have * been seen after SYSCALL_WORK_SECCOMP was seen. */ - rmb(); + smp_rmb(); if (!sd) { populate_seccomp_data(&sd_local);
According to kees's suggest, we started with the patch that just replaces rmb() with smp_rmb() and did a performace test with UnixBench. The results showed the overhead about 2.53% in rmb() test compared to the smp_rmb() one, in a x86-64 kernel with CONFIG_SMP enabled running inside a qemu-kvm vm. The test is a "syscall" testcase in UnixBench, which executes 5 syscalls in a loop during a certain timeout (100 second in our test) and counts the total number of executions of this 5-syscall sequence. We set a seccomp filter with all allow rule for all used syscalls in this test (which will go bitmap path) to make sure the rmb() will be executed. The details for the test: with rmb(): /txm # ./syscall_allow_min 100 COUNT|35861159|1|lps /txm # ./syscall_allow_min 100 COUNT|35545501|1|lps /txm # ./syscall_allow_min 100 COUNT|35664495|1|lps with smp_rmb(): /txm # ./syscall_allow_min 100 COUNT|36552771|1|lps /txm # ./syscall_allow_min 100 COUNT|36491247|1|lps /txm # ./syscall_allow_min 100 COUNT|36504746|1|lps For a x86-64 kernel with CONFIG_SMP enabled, the smp_rmb() is just a compiler barrier() which have no impact in runtime, while rmb() is a lfence which will prevent all memory access operations (not just load according the recently claim by Intel) behind itself. We can also figure it out in disassembly: with rmb(): 0000000000001430 <__seccomp_filter>: 1430: 41 57 push %r15 1432: 41 56 push %r14 1434: 41 55 push %r13 1436: 41 54 push %r12 1438: 55 push %rbp 1439: 53 push %rbx 143a: 48 81 ec 90 00 00 00 sub $0x90,%rsp 1441: 89 7c 24 10 mov %edi,0x10(%rsp) 1445: 89 54 24 14 mov %edx,0x14(%rsp) 1449: 65 48 8b 04 25 28 00 mov %gs:0x28,%rax 1450: 00 00 1452: 48 89 84 24 88 00 00 mov %rax,0x88(%rsp) 1459: 00 145a: 31 c0 xor %eax,%eax * 145c: 0f ae e8 lfence 145f: 48 85 f6 test %rsi,%rsi 1462: 49 89 f4 mov %rsi,%r12 1465: 0f 84 42 03 00 00 je 17ad <__seccomp_filter+0x37d> 146b: 65 48 8b 04 25 00 00 mov %gs:0x0,%rax 1472: 00 00 1474: 48 8b 98 80 07 00 00 mov 0x780(%rax),%rbx 147b: 48 85 db test %rbx,%rbx with smp_rmb(); 0000000000001430 <__seccomp_filter>: 1430: 41 57 push %r15 1432: 41 56 push %r14 1434: 41 55 push %r13 1436: 41 54 push %r12 1438: 55 push %rbp 1439: 53 push %rbx 143a: 48 81 ec 90 00 00 00 sub $0x90,%rsp 1441: 89 7c 24 10 mov %edi,0x10(%rsp) 1445: 89 54 24 14 mov %edx,0x14(%rsp) 1449: 65 48 8b 04 25 28 00 mov %gs:0x28,%rax 1450: 00 00 1452: 48 89 84 24 88 00 00 mov %rax,0x88(%rsp) 1459: 00 145a: 31 c0 xor %eax,%eax 145c: 48 85 f6 test %rsi,%rsi 145f: 49 89 f4 mov %rsi,%r12 1462: 0f 84 42 03 00 00 je 17aa <__seccomp_filter+0x37a> 1468: 65 48 8b 04 25 00 00 mov %gs:0x0,%rax 146f: 00 00 1471: 48 8b 98 80 07 00 00 mov 0x780(%rax),%rbx 1478: 48 85 db test %rbx,%rbx We will go further for the next optimize patch, if you guys thinks this smp_rmb() refactor is appropriate. v1 -> v2: - only replace rmb() with smp_rmb() - provide the performance test number RFC -> v1: - replace rmb() with smp_rmb() - move the smp_rmb() logic to the middle between TIF_SECCOMP and mode Signed-off-by: wanghongzhe <wanghongzhe@huawei.com> --- kernel/seccomp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)