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Date: Fri, 9 Jan 2009 16:25:37 +0100 From: Ingo Molnar <mingo@...e.hu> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: "H. Peter Anvin" <hpa@...or.com>, Chris Mason <chris.mason@...cle.com>, Peter Zijlstra <peterz@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, paulmck@...ux.vnet.ibm.com, Gregory Haskins <ghaskins@...ell.com>, Matthew Wilcox <matthew@....cx>, Andi Kleen <andi@...stfloor.org>, Andrew Morton <akpm@...ux-foundation.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, linux-btrfs <linux-btrfs@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, Nick Piggin <npiggin@...e.de>, Peter Morreale <pmorreale@...ell.com>, Sven Dietrich <SDietrich@...ell.com> Subject: Re: [patch] measurements, numbers about CONFIG_OPTIMIZE_INLINING=y impact * Ingo Molnar <mingo@...e.hu> wrote: > > I suspect gcc has some pre-inlining heuristics that don't take > > constant folding and simplifiation into account - if you look at just > > the raw tree of the function without taking the optimization into > > account, it will look big. > > Yeah. In my tests GCC 4.3.2 does properly inline that particular asm. here is how that function ended up looking like here (with Peter's v7, which should be close to what Chris tried, looking at his crash dump): ffffffff81491347 <__mutex_lock_common>: ffffffff81491347: 55 push %rbp ffffffff81491348: 48 89 e5 mov %rsp,%rbp ffffffff8149134b: 41 57 push %r15 ffffffff8149134d: 4c 8d 7f 08 lea 0x8(%rdi),%r15 ffffffff81491351: 41 56 push %r14 ffffffff81491353: 49 89 f6 mov %rsi,%r14 ffffffff81491356: 41 55 push %r13 ffffffff81491358: 41 54 push %r12 ffffffff8149135a: 4c 8d 67 18 lea 0x18(%rdi),%r12 ffffffff8149135e: 53 push %rbx ffffffff8149135f: 48 89 fb mov %rdi,%rbx ffffffff81491362: 48 83 ec 38 sub $0x38,%rsp ffffffff81491366: 65 4c 8b 2c 25 00 00 mov %gs:0x0,%r13 ffffffff8149136d: 00 00 ffffffff8149136f: b8 01 00 00 00 mov $0x1,%eax ffffffff81491374: 31 d2 xor %edx,%edx ffffffff81491376: f0 0f b1 13 lock cmpxchg %edx,(%rbx) ffffffff8149137a: 83 f8 01 cmp $0x1,%eax ffffffff8149137d: 75 18 jne ffffffff81491397 <__mutex_lock_common+0x50> ffffffff8149137f: 65 48 8b 04 25 10 00 mov %gs:0x10,%rax ffffffff81491386: 00 00 ffffffff81491388: 48 2d d8 1f 00 00 sub $0x1fd8,%rax ffffffff8149138e: 48 89 43 18 mov %rax,0x18(%rbx) ffffffff81491392: e9 dd 00 00 00 jmpq ffffffff81491474 <__mutex_lock_common+0x12d> ffffffff81491397: 85 c0 test %eax,%eax ffffffff81491399: 79 06 jns ffffffff814913a1 <__mutex_lock_common+0x5a> ffffffff8149139b: 4c 39 7b 08 cmp %r15,0x8(%rbx) ffffffff8149139f: 75 19 jne ffffffff814913ba <__mutex_lock_common+0x73> ffffffff814913a1: 49 8b 34 24 mov (%r12),%rsi ffffffff814913a5: 48 85 f6 test %rsi,%rsi ffffffff814913a8: 74 0c je ffffffff814913b6 <__mutex_lock_common+0x6f> ffffffff814913aa: 48 89 df mov %rbx,%rdi ffffffff814913ad: e8 6c dd b9 ff callq ffffffff8102f11e <spin_on_owner> ffffffff814913b2: 85 c0 test %eax,%eax ffffffff814913b4: 74 04 je ffffffff814913ba <__mutex_lock_common+0x73> ffffffff814913b6: f3 90 pause ffffffff814913b8: eb b5 jmp ffffffff8149136f <__mutex_lock_common+0x28> ffffffff814913ba: 4c 8d 63 04 lea 0x4(%rbx),%r12 ffffffff814913be: 4c 89 e7 mov %r12,%rdi ffffffff814913c1: e8 d2 0f 00 00 callq ffffffff81492398 <_spin_lock> ffffffff814913c6: 48 8b 53 10 mov 0x10(%rbx),%rdx ffffffff814913ca: 48 8d 45 b0 lea -0x50(%rbp),%rax ffffffff814913ce: 4c 89 7d b0 mov %r15,-0x50(%rbp) ffffffff814913d2: 48 89 43 10 mov %rax,0x10(%rbx) ffffffff814913d6: 48 89 02 mov %rax,(%rdx) ffffffff814913d9: 48 89 55 b8 mov %rdx,-0x48(%rbp) ffffffff814913dd: 48 83 ca ff or $0xffffffffffffffff,%rdx ffffffff814913e1: 4c 89 6d c0 mov %r13,-0x40(%rbp) ffffffff814913e5: 48 89 d0 mov %rdx,%rax ffffffff814913e8: 87 03 xchg %eax,(%rbx) ffffffff814913ea: ff c8 dec %eax ffffffff814913ec: 74 55 je ffffffff81491443 <__mutex_lock_common+0xfc> ffffffff814913ee: 44 88 f0 mov %r14b,%al ffffffff814913f1: 44 89 f2 mov %r14d,%edx ffffffff814913f4: 83 e0 81 and $0xffffffffffffff81,%eax ffffffff814913f7: 83 e2 01 and $0x1,%edx ffffffff814913fa: 88 45 af mov %al,-0x51(%rbp) ffffffff814913fd: 89 55 a8 mov %edx,-0x58(%rbp) ffffffff81491400: 48 83 c8 ff or $0xffffffffffffffff,%rax ffffffff81491404: 87 03 xchg %eax,(%rbx) ffffffff81491406: ff c8 dec %eax ffffffff81491408: 74 39 je ffffffff81491443 <__mutex_lock_common+0xfc> ffffffff8149140a: 80 7d af 00 cmpb $0x0,-0x51(%rbp) ffffffff8149140e: 74 1c je ffffffff8149142c <__mutex_lock_common+0xe5> ffffffff81491410: 49 8b 45 08 mov 0x8(%r13),%rax ffffffff81491414: f6 40 10 04 testb $0x4,0x10(%rax) ffffffff81491418: 74 12 je ffffffff8149142c <__mutex_lock_common+0xe5> ffffffff8149141a: 83 7d a8 00 cmpl $0x0,-0x58(%rbp) ffffffff8149141e: 75 65 jne ffffffff81491485 <__mutex_lock_common+0x13e> ffffffff81491420: 4c 89 ef mov %r13,%rdi ffffffff81491423: e8 e1 2e bb ff callq ffffffff81044309 <__fatal_signal_pending> ffffffff81491428: 85 c0 test %eax,%eax ffffffff8149142a: 75 59 jne ffffffff81491485 <__mutex_lock_common+0x13e> ffffffff8149142c: 4d 89 75 00 mov %r14,0x0(%r13) ffffffff81491430: 41 fe 04 24 incb (%r12) ffffffff81491434: e8 e9 ef ff ff callq ffffffff81490422 <schedule> ffffffff81491439: 4c 89 e7 mov %r12,%rdi ffffffff8149143c: e8 57 0f 00 00 callq ffffffff81492398 <_spin_lock> ffffffff81491441: eb bd jmp ffffffff81491400 <__mutex_lock_common+0xb9> ffffffff81491443: 48 8b 45 b8 mov -0x48(%rbp),%rax ffffffff81491447: 48 8b 55 b0 mov -0x50(%rbp),%rdx ffffffff8149144b: 48 89 10 mov %rdx,(%rax) ffffffff8149144e: 48 89 42 08 mov %rax,0x8(%rdx) ffffffff81491452: 65 48 8b 04 25 10 00 mov %gs:0x10,%rax ffffffff81491459: 00 00 ffffffff8149145b: 48 2d d8 1f 00 00 sub $0x1fd8,%rax ffffffff81491461: 4c 39 7b 08 cmp %r15,0x8(%rbx) ffffffff81491465: 48 89 43 18 mov %rax,0x18(%rbx) ffffffff81491469: 75 06 jne ffffffff81491471 <__mutex_lock_common+0x12a> ffffffff8149146b: c7 03 00 00 00 00 movl $0x0,(%rbx) ffffffff81491471: fe 43 04 incb 0x4(%rbx) ffffffff81491474: 31 c0 xor %eax,%eax ffffffff81491476: 48 83 c4 38 add $0x38,%rsp ffffffff8149147a: 5b pop %rbx ffffffff8149147b: 41 5c pop %r12 ffffffff8149147d: 41 5d pop %r13 ffffffff8149147f: 41 5e pop %r14 ffffffff81491481: 41 5f pop %r15 ffffffff81491483: c9 leaveq ffffffff81491484: c3 retq ffffffff81491485: 48 8b 55 b0 mov -0x50(%rbp),%rdx ffffffff81491489: 48 8b 45 b8 mov -0x48(%rbp),%rax ffffffff8149148d: 48 89 42 08 mov %rax,0x8(%rdx) ffffffff81491491: 48 89 10 mov %rdx,(%rax) ffffffff81491494: fe 43 04 incb 0x4(%rbx) ffffffff81491497: b8 fc ff ff ff mov $0xfffffffc,%eax ffffffff8149149c: eb d8 jmp ffffffff81491476 <__mutex_lock_common+0x12f> the "lock cmpxchg" ended up being inlined properly at ffffffff81491376, and the whole assembly sequence looks pretty compact to me. That does not let GCC off the hook though, and i'd be the last one to defend it when it messes up. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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