From: Jeff Garzik <jgarzik@mandrakesoft.com>
To: Anton Blanchard <anton@samba.org>
Cc: David Schwartz <davids@webmaster.com>, linux-kernel@vger.kernel.org
Subject: Re: likely/unlikely
Date: Wed, 16 Jan 2002 04:12:16 -0500 [thread overview]
Message-ID: <3C4543F0.29CCD025@mandrakesoft.com> (raw)
In-Reply-To: <3C450C4A.8A8382A6@mandrakesoft.com> <20020116060014.GB24266@krispykreme>
Anton Blanchard wrote:
>
>
> > likely/unlikely set the branch prediction values to 99% or 1%
> > respectively. If this causes the code generated to perform less
> > optimally than without, I'm sure the gcc guys would be -very- interested
> > to hear that...
>
> On some ppc64 the branch prediction is quite good and static prediction
> will override the dynamic prediction. I think we avoid predicting a
> branch unless we are quite sure (95%/5%).
>
> So if likely/unlikely is overused (on more marginal conditionals) then
> it could be a performance loss.
oh agreed... but marginal conditionals should not be getting
likely()/unlikely() as you are then lying to the compiler about the true
branch predictability...
Jeff
--
Jeff Garzik | Alternate titles for LOTR:
Building 1024 | Fast Times at Uruk-Hai
MandrakeSoft | The Took, the Elf, His Daughter and Her Lover
| Samwise Gamgee: International Hobbit of Mystery
next prev parent reply other threads:[~2002-01-16 9:14 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-01-16 3:22 likely/unlikely David Schwartz
2002-01-16 5:14 ` likely/unlikely Jeff Garzik
2002-01-16 6:00 ` likely/unlikely Anton Blanchard
2002-01-16 9:12 ` Jeff Garzik [this message]
2002-01-16 6:32 ` likely/unlikely Craig Christophel
2002-01-16 7:38 ` likely/unlikely Adrian Bunk
2002-01-16 9:14 ` likely/unlikely Jeff Garzik
2002-01-16 9:29 ` likely/unlikely Jens Axboe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3C4543F0.29CCD025@mandrakesoft.com \
--to=jgarzik@mandrakesoft.com \
--cc=anton@samba.org \
--cc=davids@webmaster.com \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.