From: Jason Baron <jbaron@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
a.p.zijlstra@chello.nl, mathieu.desnoyers@efficios.com,
davem@davemloft.net, ddaney.cavm@gmail.com,
akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs
Date: Wed, 22 Feb 2012 10:42:07 -0500 [thread overview]
Message-ID: <20120222154206.GA3405@redhat.com> (raw)
In-Reply-To: <1329923533.25686.106.camel@gandalf.stny.rr.com>
On Wed, Feb 22, 2012 at 10:12:13AM -0500, Steven Rostedt wrote:
> On Wed, 2012-02-22 at 15:56 +0100, Ingo Molnar wrote:
>
> > > Because it really just looks like a stronger "unlikely()" and
> > > fundamentally it really isn't. [...]
> >
> > Well, the fact is that right now it *is* a stronger unlikely()
> > on architectures that have jump-labels and it's mapped to
> > unlikely() on others.
> >
>
> Has gcc been fix to make it truly an unlikely case and remove the "jmp;
> jmp" problem of before? I'm still using gcc 4.6.0 which has the
> following code for a tracepoint (example is the
> trace_sched_migrate_task().
>
> 5b4a: e9 00 00 00 00 jmpq 5b4f <set_task_cpu+0x5e>
>
> The above is the jump label that turns into a nop at boot up.
>
> 5b4f: eb 19 jmp 5b6a <set_task_cpu+0x79>
>
> Here we jump over some of the trace code (this is the fast path)
>
> 5b51: 49 8b 7d 08 mov 0x8(%r13),%rdi
> 5b55: 44 89 e2 mov %r12d,%edx
> 5b58: 48 89 de mov %rbx,%rsi
> 5b5b: 41 ff 55 00 callq *0x0(%r13)
> 5b5f: 49 83 c5 10 add $0x10,%r13
> 5b63: 49 83 7d 00 00 cmpq $0x0,0x0(%r13)
> 5b68: eb 41 jmp 5bab <set_task_cpu+0xba>
>
> Below is the continuation of the fast path.
>
> 5b6a: 48 8b 43 08 mov 0x8(%rbx),%rax
> 5b6e: 44 39 60 18 cmp %r12d,0x18(%rax)
> 5b72: 74 0c je 5b80 <set_task_cpu+0x8f>
>
>
> Again, I'm using gcc 4.6.0 and maybe it has been fixed.
>
> -- Steve
>
>
Hi Steve,
Using 4.6.2, I don't see the 'jmp;jmp' issue. I have:
ffffffff810610c0 <set_task_cpu>:
ffffffff810610c0: 55 push %rbp
ffffffff810610c1: 48 89 e5 mov %rsp,%rbp
ffffffff810610c4: 48 81 ec e0 00 00 00 sub $0xe0,%rsp
ffffffff810610cb: 48 89 5d d8 mov %rbx,-0x28(%rbp)
ffffffff810610cf: 4c 89 65 e0 mov %r12,-0x20(%rbp)
ffffffff810610d3: 48 89 fb mov %rdi,%rbx
ffffffff810610d6: 4c 89 6d e8 mov %r13,-0x18(%rbp)
ffffffff810610da: 4c 89 75 f0 mov %r14,-0x10(%rbp)
ffffffff810610de: 41 89 f4 mov %esi,%r12d
ffffffff810610e1: 4c 89 7d f8 mov %r15,-0x8(%rbp)
no double jump here.
ffffffff810610e5: e9 00 00 00 00 jmpq ffffffff810610ea <set_task_cpu+0x2a>
ffffffff810610ea: 48 8b 43 08 mov 0x8(%rbx),%rax
ffffffff810610ee: 44 3b 60 18 cmp 0x18(%rax),%r12d
ffffffff810610f2: 74 0d je ffffffff81061101 <set_task_cpu+0x41>
ffffffff810610f4: 48 83 83 a8 00 00 00 addq $0x1,0xa8(%rbx)
ffffffff810610fb: 01
no double jump here.
ffffffff810610fc: e9 00 00 00 00 jmpq ffffffff81061101 <set_task_cpu+0x41>
ffffffff81061101: 48 8b 83 60 06 00 00 mov 0x660(%rbx),%rax
ffffffff81061108: 48 8b 50 40 mov 0x40(%rax),%rdx
ffffffff8106110c: 44 89 e0 mov %r12d,%eax
ffffffff8106110f: 48 8b 4a 28 mov 0x28(%rdx),%rcx
ffffffff81061113: 48 8b 0c c1 mov (%rcx,%rax,8),%rcx
ffffffff81061117: 48 89 8b 90 01 00 00 mov %rcx,0x190(%rbx)
ffffffff8106111e: 48 8b 52 20 mov 0x20(%rdx),%rdx
ffffffff81061122: 48 8b 04 c2 mov (%rdx,%rax,8),%rax
ffffffff81061126: 48 89 83 88 01 00 00 mov %rax,0x188(%rbx)
ffffffff8106112d: 48 8b 43 08 mov 0x8(%rbx),%rax
ffffffff81061131: 44 89 60 18 mov %r12d,0x18(%rax)
ffffffff81061135: 48 8b 5d d8 mov -0x28(%rbp),%rbx
ffffffff81061139: 4c 8b 65 e0 mov -0x20(%rbp),%r12
ffffffff8106113d: 4c 8b 6d e8 mov -0x18(%rbp),%r13
ffffffff81061141: 4c 8b 75 f0 mov -0x10(%rbp),%r14
ffffffff81061145: 4c 8b 7d f8 mov -0x8(%rbp),%r15
ffffffff81061149: c9 leaveq
ffffffff8106114a: c3 retq
....
Do you have 'CONFIG_CC_OPTIMIZE_FOR_SIZE' set?
Thanks,
-Jason
next prev parent reply other threads:[~2012-02-22 15:42 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-21 20:02 [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs Jason Baron
2012-02-21 20:02 ` [PATCH 01/10] jump label: Add a WARN() if jump label key count goes negative Jason Baron
2012-02-29 10:13 ` [tip:perf/core] " tip-bot for Jason Baron
2012-02-21 20:02 ` [PATCH 02/10] jump label: fix compiler warning Jason Baron
2012-02-29 10:14 ` [tip:perf/core] jump label: Fix " tip-bot for Jason Baron
2012-02-21 20:03 ` [PATCH 03/10] jump label: introduce very_unlikely() Jason Baron
2012-02-21 20:03 ` [PATCH 04/10] jump label: introduce very_likely() Jason Baron
2012-02-21 20:03 ` [PATCH 05/10] perf: update to use 'very_unlikely()' Jason Baron
2012-02-21 20:03 ` [PATCH 06/10] tracepoints: update to use very_unlikely() Jason Baron
2012-02-21 20:03 ` [PATCH 07/10] sched: update to use very_[un]likely() Jason Baron
2012-02-21 20:03 ` [PATCH 08/10] kvm: update to use very_unlikely() Jason Baron
2012-02-21 20:03 ` [PATCH 09/10] net: " Jason Baron
2012-02-21 20:03 ` [PATCH 10/10] jump label: Add docs better explaining the whole jump label mechanism Jason Baron
2012-02-29 10:15 ` [tip:perf/core] static keys: Add docs better explaining the whole 'struct static_key' mechanism tip-bot for Jason Baron
2012-02-21 20:09 ` [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs H. Peter Anvin
2012-02-21 20:20 ` Jason Baron
2012-02-21 20:39 ` Steven Rostedt
2012-02-21 21:10 ` H. Peter Anvin
2012-02-21 21:16 ` Mathieu Desnoyers
2012-02-21 21:11 ` Mathieu Desnoyers
2012-02-22 7:32 ` Ingo Molnar
2012-02-22 7:53 ` Ingo Molnar
2012-02-22 8:01 ` H. Peter Anvin
2012-02-22 8:18 ` Ingo Molnar
2012-02-22 8:58 ` [PATCH] static keys: Introduce 'struct static_key', very_[un]likely(), static_key_slow_[inc|dec]() Ingo Molnar
2012-02-29 10:16 ` [tip:perf/core] static keys: Introduce 'struct static_key', static_key_true()/false() and static_key_slow_[inc|dec]() tip-bot for Ingo Molnar
2012-02-22 9:03 ` [PATCH] jump labels: Explain the .config option better Ingo Molnar
2012-02-22 15:08 ` [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs H. Peter Anvin
2012-02-22 15:51 ` Ingo Molnar
2012-02-22 21:33 ` Paul Mackerras
2012-02-23 10:02 ` Ingo Molnar
2012-02-23 16:21 ` Jason Baron
2012-02-23 17:10 ` H. Peter Anvin
2012-02-24 9:11 ` Ingo Molnar
2012-02-23 17:18 ` Linus Torvalds
2012-02-23 22:33 ` Ingo Molnar
2012-02-23 22:39 ` Ingo Molnar
2012-02-23 22:44 ` Steven Rostedt
2012-02-23 23:18 ` Mathieu Desnoyers
2012-02-24 2:25 ` Jason Baron
2012-02-24 9:08 ` Ingo Molnar
2012-02-24 15:35 ` Jason Baron
2012-02-27 7:40 ` Ingo Molnar
2012-02-24 15:51 ` Mathieu Desnoyers
2012-02-24 16:06 ` Steven Rostedt
2012-02-24 7:52 ` static keys: Introduce 'struct static_key', static_key_true()/false() and static_key_slow_[inc|dec]() Ingo Molnar
2012-02-24 7:59 ` [PATCH] " Ingo Molnar
2012-02-24 7:54 ` [PATCH] static keys: Add docs better explaining the whole 'struct static_key' mechanism Ingo Molnar
2012-02-23 22:45 ` [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs Linus Torvalds
2012-02-24 8:04 ` Ingo Molnar
2012-02-24 2:42 ` Jason Baron
2012-02-21 20:21 ` Steven Rostedt
2012-02-21 21:11 ` H. Peter Anvin
2012-02-22 6:50 ` Ingo Molnar
2012-02-22 7:03 ` H. Peter Anvin
2012-02-22 7:25 ` Ingo Molnar
2012-02-22 7:35 ` H. Peter Anvin
2012-02-22 7:48 ` Ingo Molnar
2012-02-22 7:55 ` H. Peter Anvin
2012-02-22 8:06 ` Ingo Molnar
2012-02-22 13:22 ` Steven Rostedt
2012-02-22 13:34 ` Ingo Molnar
2012-02-22 13:54 ` Steven Rostedt
2012-02-22 14:20 ` Mathieu Desnoyers
2012-02-22 14:36 ` Steven Rostedt
2012-02-22 14:56 ` Ingo Molnar
2012-02-22 15:11 ` H. Peter Anvin
2012-02-22 15:11 ` Peter Zijlstra
2012-02-22 15:47 ` Ingo Molnar
2012-02-22 15:12 ` Steven Rostedt
2012-02-22 15:15 ` H. Peter Anvin
2012-02-22 15:19 ` H. Peter Anvin
2012-02-22 15:42 ` Jason Baron [this message]
2012-02-22 15:54 ` Steven Rostedt
2012-02-22 15:56 ` Jason Baron
2012-02-22 16:08 ` Steven Rostedt
2012-02-22 15:19 ` Jason Baron
2012-02-22 15:40 ` H. Peter Anvin
2012-02-22 15:13 ` Peter Zijlstra
2012-02-22 15:32 ` Peter Zijlstra
2012-02-22 17:14 ` Richard Henderson
2012-02-22 18:28 ` H. Peter Anvin
2012-02-22 18:58 ` Jason Baron
2012-02-22 19:10 ` H. Peter Anvin
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