Messages in this thread | | | Date | Tue, 3 Sep 2013 14:34:38 -0700 | Subject | Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount | From | Linus Torvalds <> |
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On Tue, Sep 3, 2013 at 2:13 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > This is the one that actually compiles. Whether it *works* is still a > total mystery.
It generates ok code, and it booted, so it seems to work at least for my config.
However, it seems to make no performance-difference what-so-ever, and lg_local_lock is still using about 7% cpu per the profiles.
The code generation is slightly better, but the profile looks the same:
│ ffffffff81078e70 <lg_local_lock>: 0.62 │ push %rbp 0.28 │ mov %rsp,%rbp 0.22 │ add %gs:0xcd48,%rdi 0.27 │ mov $0x100,%eax 97.22 │ lock xadd %ax,(%rdi) 0.01 │ movzbl %ah,%edx │ cmp %al,%dl 0.56 │ ↓ je 29 │ xchg %ax,%ax 0.00 │20: pause 0.00 │ movzbl (%rdi),%eax │ cmp %dl,%al │ ↑ jne 20 │29: pop %rbp 0.81 │ ← retq
but it still obviously doesn't do the "lock xadd %ax,%gs:(%rdi)" (without the preceding 'add') that would be the optimal code.
I'll try to hack that up too, but it's looking like it really is just the "lock xadd", not the memory dependency chain..
Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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