Messages in this thread | | | From | Eric Dumazet <> | Date | Fri, 26 May 2023 20:55:22 +0200 | Subject | Re: x86 copy performance regression |
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On Fri, May 26, 2023 at 8:33 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Fri, May 26, 2023 at 10:51 AM Eric Dumazet <edumazet@google.com> wrote: > > > > Hmmm > > > > [ 25.532236] RIP: 0010:0xffffffffa5a85134 > > [ 25.536173] Code: Unable to access opcode bytes at 0xffffffffa5a8510a. > > This was the other reason I really didn't want to use alternatives on > the conditional branch instructions. The relocations are really not > very natural, and we have odd rules for those things. So I suspect our > instruction rewriting simply gets this wrong, because that's such a > nasty pattern. > > I really wanted my "just hardcode the instruction bytes" to work. Not > only did it get me the small 2-byte conditional jump, it meant that > there was no relocation on it. But objtool really hates not > understanding what the alternatives code does. > > Which is fair enough, but it's frustrating here when it only results > in more problems. > > Anyway, I guess *this* avoids all issues. It creates an extra jump to > a jump for the case where the CPU doesn't have ERMS, but I guess we > don't really care about those CPUs anyway. > > And it avoids all the "alternative instructions have relocations" > issues. And it creates all small two-byte jumps, and the "rep movsb" > fits exactly on that same 2 bytes too. Which I guess all argues for > this being what I should have started with. > > This time it *really* works. >
Indeed, this one is working and fixes the issue for me, thanks a lot !
New numbers look similar to 6.3 ones.
Tested-by: Eric Dumazet <edumazet@google.com>
Performance counter stats for 'taskset 02 ./tcp_mmap -H 2002:a05:6608:297::':
2,833.29 msec task-clock # 0.970 CPUs utilized 1,065 context-switches # 375.888 /sec 1 cpu-migrations # 0.353 /sec 128 page-faults # 45.177 /sec 10,297,389,329 cycles # 3.634 GHz 7,213,189,594 instructions # 0.70 insn per cycle 1,220,821,121 branches # 430.884 M/sec 10,430,907 branch-misses # 0.85% of all branches
2.921180547 seconds time elapsed
0.005304000 seconds user 2.478561000 seconds sys
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