From: David Laight <David.Laight@ACULAB.COM>
To: 'Peter Zijlstra' <peterz@infradead.org>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.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>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"dvyukov@google.com" <dvyukov@google.com>,
"rostedt@goodmis.org" <rostedt@goodmis.org>
Subject: RE: [PATCH 02/25] tracing: Improve "if" macro code generation
Date: Wed, 20 Mar 2019 11:18:46 +0000 [thread overview]
Message-ID: <f918ecb0b6bf43f3bf0f526084d8467b@AcuMS.aculab.com> (raw)
In-Reply-To: <20190318155140.058627431@infradead.org>
From: > Peter Zijlstra
> Sent: 18 March 2019 15:39
>
> 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.
>
> Make it easier for GCC to optimize by keeping the conditional as a
> conditional rather than converting it to an integer. This shrinks the
> generated code quite a bit, and also makes the code sane enough for
> objtool to understand.
...
> include/linux/compiler.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_
> .line = __LINE__, \
> }; \
> ______r = !!(cond); \
Is that (or maybe just the !!) needed any more??
> - ______f.miss_hit[______r]++; \
> + ______r ? ______f.miss_hit[1]++ : ______f.miss_hit[0]++;\
> ______r; \
> }))
> #endif /* CONFIG_PROFILE_ALL_BRANCHES */
>
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2019-03-20 11:17 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 [this message]
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
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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