From: Guenter Roeck <linux@roeck-us.net>
To: Richard Weinberger <richard@nod.at>, Li RongQing <roy.qing.li@gmail.com>
Cc: linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
fabf@skynet.be, jkosina@suse.cz,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
oleg@redhat.com, akpm@linux-foundation.org
Subject: Re: [RFC][PATCH] signal: replace !likely with unlikely!
Date: Sat, 13 Sep 2014 06:28:18 -0700 [thread overview]
Message-ID: <54144672.9060807@roeck-us.net> (raw)
In-Reply-To: <541416AB.7000808@nod.at>
On 09/13/2014 03:04 AM, Richard Weinberger wrote:
> Am 13.09.2014 04:48, schrieb Li RongQing:
>> I did not test, how to test it?
>
> Compare the object files of both variants to find out whether both create
> semantically equivalent code and whether the un/likely have an effect.
> i.e. objdump -S -d kernel/signal.o
> I guess you can just remove the likely as gcc is smart enough to detect the "goto ret;"
> as an unlikely taken branch.
>
Or just write similar test code and observe the result.
When you are doing that, you might learn that if "(!likely(expression))"
is _not_ the same as "if (unlikely(!expression))".
Guenter
prev parent reply other threads:[~2014-09-13 13:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-11 0:48 [RFC][PATCH] signal: replace !likely with unlikely! roy.qing.li
2014-09-11 19:18 ` Guenter Roeck
2014-09-13 2:48 ` Li RongQing
2014-09-13 10:04 ` Richard Weinberger
2014-09-13 13:28 ` Guenter Roeck [this message]
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