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From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Jason Baron <jbaron@akamai.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>, Nadav Amit <namit@vmware.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	"H.J. Lu" <hjl.tools@gmail.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH v4 14/18] static_call: Add static_cond_call()
Date: Wed, 6 May 2020 12:57:02 -0700	[thread overview]
Message-ID: <88AE3649-C2E6-4965-86B5-C8FE9D226293@amacapital.net> (raw)
In-Reply-To: <CAHk-=wjdLY-E3m21_QcHUauakW3qAAOCe2rxzuFEm-Af_oqG0g@mail.gmail.com>



> On May 6, 2020, at 10:23 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 
> On Wed, May 6, 2020 at 6:51 AM Peter Zijlstra <peterz@infradead.org> wrote:
>> 
>> I was hoping for:
>> 
>>        bar:                                    # @bar
>>                movl    %edi, .L_x$local(%rip)
>>                retq
>>        ponies:                                 # @ponies
>>                movq    .Lfoo$local(%rip), %rax
>>                testq   %rax, %rax
>>                jz      1f
>>                jmpq    *%rcx                   # TAILCALL
>>        1:
>>                retq
> 
> If you want to just avoid the 'cmov', the best way to do that is to
> insert a barrier() on one side of the if-statement.
> 
> That breaks the ability to turn the conditional jump into a cmov.

Having done this in the past, you can get potentially better code with asm volatile (“”); than with a barrier and its memory clobber. I don’t know if that will make a difference in this particular case.

  reply	other threads:[~2020-05-06 19:57 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-01 20:28 [PATCH v4 00/18] Add static_call() Peter Zijlstra
2020-05-01 20:28 ` [PATCH v4 01/18] notifier: Fix broken error handling pattern Peter Zijlstra
2020-05-01 23:35   ` Steven Rostedt
2020-05-01 20:28 ` [PATCH v4 02/18] module: Fix up module_notifier return values Peter Zijlstra
2020-05-01 20:28 ` [PATCH v4 03/18] module: Properly propagate MODULE_STATE_COMING failure Peter Zijlstra
2020-05-01 20:28 ` [PATCH v4 04/18] jump_label,module: Fix module lifetime for __jump_label_mod_text_reserved Peter Zijlstra
2020-05-01 20:28 ` [PATCH v4 05/18] compiler.h: Make __ADDRESSABLE() symbol truly unique Peter Zijlstra
2020-05-01 20:28 ` [PATCH v4 06/18] static_call: Add basic static call infrastructure Peter Zijlstra
2020-05-05 21:21   ` Josh Poimboeuf
2020-05-01 20:28 ` [PATCH v4 07/18] static_call: Add inline " Peter Zijlstra
2020-05-05 22:10   ` Josh Poimboeuf
2020-05-06 16:15     ` Peter Zijlstra
2020-05-01 20:28 ` [PATCH v4 08/18] static_call: Avoid kprobes on inline static_call()s Peter Zijlstra
2020-05-01 20:28 ` [PATCH v4 09/18] x86/static_call: Add out-of-line static call implementation Peter Zijlstra
2020-05-06 16:16   ` Peter Zijlstra
2020-05-01 20:28 ` [PATCH v4 10/18] x86/static_call: Add inline static call implementation for x86-64 Peter Zijlstra
2020-05-01 20:29 ` [PATCH v4 11/18] static_call: Simple self-test Peter Zijlstra
2020-05-01 20:29 ` [PATCH v4 12/18] tracepoint: Optimize using static_call() Peter Zijlstra
2020-05-13  8:48   ` [tracepoint] 01edfaf177: WARNING:at_kernel/static_call.c:#__static_call_update kernel test robot
2020-05-15 17:13     ` Peter Zijlstra
2020-05-01 20:29 ` [PATCH v4 13/18] x86/alternatives: Teach text_poke_bp() to emulate RET Peter Zijlstra
2020-05-01 20:29 ` [PATCH v4 14/18] static_call: Add static_cond_call() Peter Zijlstra
2020-05-02 13:08   ` Rasmus Villemoes
2020-05-03 12:58     ` Peter Zijlstra
2020-05-04  7:20       ` Rasmus Villemoes
2020-05-04 20:14         ` Peter Zijlstra
2020-05-05  7:50           ` Rasmus Villemoes
2020-05-05  9:38             ` Peter Zijlstra
2020-05-05  9:36           ` Peter Zijlstra
2020-05-05 18:13             ` Nick Desaulniers
2020-05-05 18:27               ` Nick Desaulniers
2020-05-05 18:48                 ` Linus Torvalds
2020-05-05 19:00                   ` Mathieu Desnoyers
2020-05-05 19:57                     ` Nick Desaulniers
2020-05-05 20:27                       ` Mathieu Desnoyers
2020-05-06 13:55                         ` Peter Zijlstra
2020-05-06 14:01                           ` Mathieu Desnoyers
2020-05-06 16:18                             ` Peter Zijlstra
2020-05-06 13:51               ` Peter Zijlstra
2020-05-06 16:00                 ` Peter Zijlstra
2020-05-06 17:16                 ` Linus Torvalds
2020-05-06 19:57                   ` Andy Lutomirski [this message]
2020-05-06 17:24   ` Josh Poimboeuf
2020-05-06 17:58     ` Peter Zijlstra
2020-05-06 18:09       ` Josh Poimboeuf
2020-05-06 18:16         ` Peter Zijlstra
2020-05-08 15:27     ` Peter Zijlstra
2020-05-08 15:47       ` Josh Poimboeuf
2020-05-08 16:17         ` Peter Zijlstra
2020-05-01 20:29 ` [PATCH v4 15/18] static_call: Handle tail-calls Peter Zijlstra
2020-05-06 18:10   ` Peter Zijlstra
2020-05-01 20:29 ` [PATCH v4 16/18] static_call: Allow early init Peter Zijlstra
2020-05-06 21:15   ` Josh Poimboeuf
2020-05-08 13:31     ` Peter Zijlstra
2020-05-08 14:27       ` Josh Poimboeuf
2020-05-08 15:30         ` Peter Zijlstra
2020-05-01 20:29 ` [PATCH v4 17/18] x86/perf, static_call: Optimize x86_pmu methods Peter Zijlstra
2020-05-01 20:29 ` [PATCH v4 18/18] objtool: Clean up elf_write() condition Peter Zijlstra
2020-05-06 17:32 ` [PATCH v4 00/18] Add static_call() Josh Poimboeuf
2020-05-06 18:05   ` Peter Zijlstra

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