From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
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>,
"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 13:45:31 -0500 [thread overview]
Message-ID: <20190509184531.jhinxi2x2pdfaefb@treble> (raw)
In-Reply-To: <20190509142902.08a32f20@gandalf.local.home>
On Thu, May 09, 2019 at 02:29:02PM -0400, Steven Rostedt wrote:
> 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>
Actually, my original fix already went in:
37686b1353cf ("tracing: Improve "if" macro code generation")
But it introduced a regression:
https://lkml.kernel.org/r/201905040509.iqQ2CrOU%lkp@intel.com
which Linus' patch fixes for some reason.
--
Josh
next prev parent reply other threads:[~2019-05-09 18:45 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
2019-05-09 18:45 ` Josh Poimboeuf [this message]
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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