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From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Laight <David.Laight@aculab.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"julien.thierry@arm.com" <julien.thierry@arm.com>,
	"will.deacon@arm.com" <will.deacon@arm.com>,
	"luto@amacapital.net" <luto@amacapital.net>,
	"mingo@kernel.org" <mingo@kernel.org>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"james.morse@arm.com" <james.morse@arm.com>,
	"valentin.schneider@arm.com" <valentin.schneider@arm.com>,
	"brgerst@gmail.com" <brgerst@gmail.com>,
	"jpoimboe@redhat.com" <jpoimboe@redhat.com>,
	"luto@kernel.org" <luto@kernel.org>,
	"bp@alien8.de" <bp@alien8.de>,
	"dvlasenk@redhat.com" <dvlasenk@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"dvyukov@google.com" <dvyukov@google.com>
Subject: Re: [PATCH 02/25] tracing: Improve "if" macro code generation
Date: Thu, 9 May 2019 14:29:02 -0400	[thread overview]
Message-ID: <20190509142902.08a32f20@gandalf.local.home> (raw)
In-Reply-To: <CAHk-=wiLMXDO-_NGjgtoHxp9TRpcnykHPNWOHfXfWd9GmCu1Uw@mail.gmail.com>

On Thu, 9 May 2019 09:51:59 -0700
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Thu, May 9, 2019 at 6:01 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > This patch works. Can I get your Signed-off-by for it?  
> 
> Yes. Please write some kind of comprehensible commit log for it, but

How's this:

"Peter Zijlstra noticed that with CONFIG_PROFILE_ALL_BRANCHES, the "if"
macro converts the conditional to an array index.  This can cause GCC
to create horrible code.  When there are nested ifs, the generated code
uses register values to encode branching decisions.

Josh Poimboeuf found that replacing the define "if" macro from using
the condition as an array index and incrementing the branch statics
with an if statement itself, reduced the asm complexity and shrinks the
generated code quite a bit.

But this can be simplified even further by replacing the internal if
statement with a ternary operator.

Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: Josh Poimboeuf <jpoimboe@redhat.com>
"

> 
>    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Thanks,

-- Steve

> 
> for the patch itself.
> 

  reply	other threads:[~2019-05-09 18:29 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-18 15:38 [PATCH 00/25] objtool: UACCESS validation v4 Peter Zijlstra
2019-03-18 15:38 ` [PATCH 01/25] x86: Make SMAP 64-bit only Peter Zijlstra
2019-03-18 16:58   ` Linus Torvalds
2019-03-18 17:36     ` Peter Zijlstra
2019-03-18 17:51       ` Peter Zijlstra
2019-03-18 18:10         ` Linus Torvalds
2019-03-21 17:12           ` hpa
2019-03-21 17:25           ` Denys Vlasenko
2019-03-21 18:18             ` hpa
2019-03-21 21:03               ` Peter Zijlstra
2019-03-21 18:21             ` Linus Torvalds
2019-03-19 11:16   ` [PATCH 01/25] sched/x86: Save [ER]FLAGS on context switch Peter Zijlstra
2019-03-18 15:38 ` [PATCH 02/25] tracing: Improve "if" macro code generation Peter Zijlstra
2019-03-18 17:41   ` Steven Rostedt
2019-03-18 23:37   ` Josh Poimboeuf
2019-03-19 10:11     ` Peter Zijlstra
2019-03-20 11:18   ` David Laight
2019-03-20 17:26     ` Linus Torvalds
2019-03-20 17:37       ` David Laight
2019-03-20 17:38         ` Linus Torvalds
2019-03-20 18:18       ` Steven Rostedt
2019-05-09 13:00       ` Steven Rostedt
2019-05-09 16:51         ` Linus Torvalds
2019-05-09 18:29           ` Steven Rostedt [this message]
2019-05-09 18:45             ` Josh Poimboeuf
2019-05-09 18:47               ` Josh Poimboeuf
2019-05-09 18:48                 ` Randy Dunlap
2019-05-09 18:57                   ` Josh Poimboeuf
2019-05-09 19:06               ` Steven Rostedt
2019-05-09 19:28                 ` Steven Rostedt
2019-05-09 19:44                   ` Linus Torvalds
2019-03-18 15:38 ` [PATCH 03/25] x86/ia32: Fix ia32_restore_sigcontext AC leak Peter Zijlstra
2019-03-18 15:38 ` [PATCH 04/25] i915,uaccess: Fix redundant CLAC Peter Zijlstra
2019-03-18 15:38 ` [PATCH 05/25] x86/uaccess: Move copy_user_handle_tail into asm Peter Zijlstra
2019-03-18 15:38 ` [PATCH 06/25] x86/uaccess: Fix up the fixup Peter Zijlstra
2019-03-18 15:38 ` [PATCH 07/25] x86/nospec,objtool: Introduce ANNOTATE_IGNORE_ALTERNATIVE Peter Zijlstra
2019-03-18 15:38 ` [PATCH 08/25] x86/uaccess,xen: Suppress SMAP warnings Peter Zijlstra
2019-03-18 15:38 ` [PATCH 09/25] x86/uaccess: Always inline user_access_begin() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 10/25] x86/uaccess,signal: Fix AC=1 bloat Peter Zijlstra
2019-03-18 15:38 ` [PATCH 11/25] x86/uaccess: Introduce user_access_{save,restore}() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 12/25] x86/smap: Ditch __stringify() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 13/25] x86/uaccess,kasan: Fix KASAN vs SMAP Peter Zijlstra
2019-03-18 15:38 ` [PATCH 14/25] x86/uaccess,ubsan: Fix UBSAN " Peter Zijlstra
2019-03-18 15:38 ` [PATCH 15/25] x86/uaccess,ftrace: Fix ftrace_likely_update() " Peter Zijlstra
2019-03-18 15:38 ` [PATCH 16/25] x86/uaccess,kcov: Disable stack protector Peter Zijlstra
2019-03-18 15:38 ` [PATCH 17/25] objtool: Set insn->func for alternatives Peter Zijlstra
2019-03-18 15:38 ` [PATCH 18/25] objtool: Handle function aliases Peter Zijlstra
2019-03-18 15:38 ` [PATCH 19/25] objtool: Rewrite add_ignores() Peter Zijlstra
2019-03-18 15:39 ` [PATCH 20/25] objtool: Add --backtrace support Peter Zijlstra
2019-03-18 15:39 ` [PATCH 21/25] objtool: Rewrite alt->skip_orig Peter Zijlstra
2019-03-18 15:39 ` [PATCH 22/25] objtool: Fix sibling call detection Peter Zijlstra
2019-03-18 15:39 ` [PATCH 23/25] objtool: Add UACCESS validation Peter Zijlstra
2019-03-18 23:51   ` Josh Poimboeuf
2019-05-07 11:52   ` Peter Zijlstra
2019-03-18 15:39 ` [PATCH 24/25] objtool: uaccess PUSHF/POPF support Peter Zijlstra
2019-03-18 15:39 ` [PATCH 25/25] objtool: Add Direction Flag validation Peter Zijlstra
2019-03-18 23:57 ` [PATCH 00/25] objtool: UACCESS validation v4 Josh Poimboeuf
2019-03-19 11:20   ` Peter Zijlstra
2019-03-19 11:17 ` [PATCH 26/25] sched/x86_64: Don't save flags on context switch Peter Zijlstra

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