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Groups > linux.kernel > #1608665
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: locking/atomic: Introduce atomic_try_cmpxchg() |
| Date | 2017-03-24 17:50 +0100 |
| Message-ID | <toAzw-4jh-17@gated-at.bofh.it> (permalink) |
| References | <towPg-1DH-13@gated-at.bofh.it> <toyo1-2Pm-7@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Fri, Mar 24, 2017 at 03:21:40PM +0100, Peter Zijlstra wrote:
> On Fri, Mar 24, 2017 at 01:44:00PM +0100, Dmitry Vyukov wrote:
> > So I would suggest to change it to a safer and less surprising
> > alternative:
> >
> > diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
> > index fb961db51a2a..81fb985f51f4 100644
> > --- a/arch/x86/include/asm/cmpxchg.h
> > +++ b/arch/x86/include/asm/cmpxchg.h
> > @@ -212,7 +212,8 @@ extern void __add_wrong_size(void)
> > default: \
> > __cmpxchg_wrong_size(); \
> > } \
> > - *_old = __old; \
> > + if (!success) \
> > + *_old = __old; \
> > success; \
> > })
>
> I've no immediate objection, I'll double check what, if anything, it
> does for code gen.
So the first snipped I tested regressed like so:
0000000000000000 <T_refcount_inc>: 0000000000000000 <T_refcount_inc>:
0: 8b 07 mov (%rdi),%eax 0: 8b 17 mov (%rdi),%edx
2: 83 f8 ff cmp $0xffffffff,%eax 2: 83 fa ff cmp $0xffffffff,%edx
5: 74 13 je 1a <T_refcount_inc+0x1a> 5: 74 1a je 21 <T_refcount_inc+0x21>
7: 85 c0 test %eax,%eax 7: 85 d2 test %edx,%edx
9: 74 0d je 18 <T_refcount_inc+0x18> 9: 74 13 je 1e <T_refcount_inc+0x1e>
b: 8d 50 01 lea 0x1(%rax),%edx b: 8d 4a 01 lea 0x1(%rdx),%ecx
e: f0 0f b1 17 lock cmpxchg %edx,(%rdi) e: 89 d0 mov %edx,%eax
12: 75 ee jne 2 <T_refcount_inc+0x2> 10: f0 0f b1 0f lock cmpxchg %ecx,(%rdi)
14: ff c2 inc %edx 14: 74 04 je 1a <T_refcount_inc+0x1a>
16: 75 02 jne 1a <T_refcount_inc+0x1a> 16: 89 c2 mov %eax,%edx
18: 0f 0b ud2 18: eb e8 jmp 2 <T_refcount_inc+0x2>
1a: c3 retq 1a: ff c1 inc %ecx
1c: 75 03 jne 21 <T_refcount_inc+0x21>
1e: 0f 0b ud2
20: c3 retq
21: c3 retq
Which is rather unfortunate...
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
re: locking/atomic: Introduce atomic_try_cmpxchg() Dmitry Vyukov <dvyukov@google.com> - 2017-03-24 13:50 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Dmitry Vyukov <dvyukov@google.com> - 2017-03-24 15:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 15:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 17:50 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Andy Lutomirski <luto@amacapital.net> - 2017-03-24 18:00 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 18:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Dmitry Vyukov <dvyukov@google.com> - 2017-03-24 19:00 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 19:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 19:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Andy Lutomirski <luto@kernel.org> - 2017-03-24 20:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-24 20:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Andy Lutomirski <luto@amacapital.net> - 2017-03-24 20:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 21:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 21:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Andy Lutomirski <luto@amacapital.net> - 2017-03-24 21:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Dmitry Vyukov <dvyukov@google.com> - 2017-03-24 19:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 19:10 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 19:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Andy Lutomirski <luto@amacapital.net> - 2017-03-24 19:50 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-24 20:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 22:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-25 09:00 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-25 19:10 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-25 19:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-25 19:40 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-25 22:20 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-25 23:10 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-27 12:00 +0200
Re: locking/atomic: Introduce atomic_try_cmpxchg() Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-25 19:40 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 21:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Andy Lutomirski <luto@kernel.org> - 2017-03-24 21:30 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 22:10 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-24 20:10 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-24 21:50 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-24 22:00 +0100
Re: locking/atomic: Introduce atomic_try_cmpxchg() Peter Zijlstra <peterz@infradead.org> - 2017-03-27 14:20 +0200
Re: locking/atomic: Introduce atomic_try_cmpxchg() Dmitry Vyukov <dvyukov@google.com> - 2017-03-27 15:50 +0200
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