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From: "Tobin C. Harding" <me@tobin.cc>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
	kernel-hardening@lists.openwall.com,
	"Theodore Ts'o" <tytso@mit.edu>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Kees Cook <keescook@chromium.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Tycho Andersen <tycho@docker.com>,
	"Roberts, William C" <william.c.roberts@intel.com>,
	Tejun Heo <tj@kernel.org>,
	Jordan Glover <Golden_Miller83@protonmail.ch>,
	Petr Mladek <pmladek@suse.com>, Joe Perches <joe@perches.com>,
	Ian Campbell <ijc@hellion.org.uk>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <wilal.deacon@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Chris Fries <cfries@google.com>,
	Dave Weinstein <olorin@google.com>,
	Daniel Micay <danielmicay@gmail.com>,
	Djalal Harouni <tixxdz@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v7] printk: hash addresses printed with %p
Date: Thu, 26 Oct 2017 20:10:36 +1100	[thread overview]
Message-ID: <20171026091036.GI12341@eros> (raw)
In-Reply-To: <20171026070003.GA25583@kroah.com>

On Thu, Oct 26, 2017 at 09:00:03AM +0200, Greg KH wrote:
> On Thu, Oct 26, 2017 at 12:59:08AM +0200, Jason A. Donenfeld wrote:
> > On Thu, Oct 26, 2017 at 12:27 AM, Tobin C. Harding <me@tobin.cc> wrote:
> > > How good is unlikely()?
> > 
> > It places that branch way at the bottom of the function so that it's
> > less likely to pollute the icache.
> 
> But always measure it.  Lots of times (old numbers were 90% or so), we
> get the marking wrong, so please, always benchmark the thing to verify
> it actually is doing what you think it should be doing, otherwise it
> could make the code worse.

Does this come under 'premature optimization is the root of all evil'?

Should we be leaving out things like unlikely() and __read_only until
the code has been profiled?

thanks,
Tobin.

  reply	other threads:[~2017-10-26  9:10 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-25  4:00 [PATCH v7] printk: hash addresses printed with %p Jason A. Donenfeld
2017-10-25 10:05 ` Tobin C. Harding
2017-10-25 22:27 ` Tobin C. Harding
2017-10-25 22:59   ` Jason A. Donenfeld
2017-10-25 23:11     ` Tobin C. Harding
2017-10-26  7:00     ` Greg KH
2017-10-26  9:10       ` Tobin C. Harding [this message]
  -- strict thread matches above, loose matches on Subject: below --
2017-10-23 22:33 Tobin C. Harding
2017-10-23 23:00 ` Jason A. Donenfeld
2017-10-24  0:31   ` Tobin C. Harding
2017-10-24 11:25     ` Jason A. Donenfeld
2017-10-24 20:45       ` Tobin C. Harding
2017-10-25  3:49       ` Tobin C. Harding
2017-10-30 20:22         ` Steven Rostedt
2017-10-30 21:24           ` Tobin C. Harding
2017-10-31 14:22           ` Jason A. Donenfeld
     [not found] ` <87bmkw5owv.fsf@rasmusvillemoes.dk>
     [not found]   ` <20171024235755.GA15832@eros>
2017-10-25 19:02     ` Rasmus Villemoes
2017-10-25 22:14       ` Tobin C. Harding

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