From: Grant Grundler <iod00d@hp.com>
To: linux-ia64@vger.kernel.org
Subject: Re: [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random problem on 2.6.12-rc1)]
Date: Sat, 09 Apr 2005 00:46:03 +0000 [thread overview]
Message-ID: <20050409004603.GJ3844@esmail.cup.hp.com> (raw)
In-Reply-To: <20050408103324.6c5231df.akpm@osdl.org>
On Fri, Apr 08, 2005 at 04:15:43PM -0700, Matt Mackall wrote:
> > static inline int
> > fls (int x)
> > {
> > if (!x)
> > return 0;
> > return ia64_fls((unsigned int) x) + 1;
> > }
>
> I was trying desperately to avoid the branch, as I understand there
> are issues there on IA64.
ia64 will inline this routine (no return branch) and the "if ()" case
will be predicated (which is very efficient).
parisc/et al pay a penalty for un-/mis-predicted branches.
But not as bad a cache miss by a long shot.
Adding "likely()" (or unlikely as approrpiate) can help
mitigate where the compiler doesn't pick the right thing.
grant
next prev parent reply other threads:[~2005-04-09 0:46 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-04-08 17:33 [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random Andrew Morton
2005-04-08 17:48 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random problem on 2.6.12-rc1)] Matt Mackall
2005-04-08 18:02 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random Andrew Morton
2005-04-08 19:05 ` David Mosberger
2005-04-08 20:46 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random problem on 2.6.12-rc1)] David Mosberger
2005-04-08 22:49 ` Matt Mackall
2005-04-08 23:01 ` David Mosberger
2005-04-08 23:02 ` Luck, Tony
2005-04-08 23:15 ` Matt Mackall
2005-04-08 23:17 ` Matt Mackall
2005-04-08 23:19 ` David Mosberger
2005-04-08 23:49 ` David Mosberger
2005-04-09 0:21 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random David Mosberger
2005-04-09 0:28 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random problem on 2.6.12-rc1)] Matt Mackall
2005-04-09 0:34 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random Arthur Kepner
2005-04-09 0:46 ` Grant Grundler [this message]
2005-04-09 3:00 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random problem on 2.6.12-rc1)] Grant Grundler
2005-04-09 4:05 ` David Mosberger
2005-04-09 4:32 ` David Mosberger
2005-04-09 5:09 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random David Mosberger
2005-04-09 5:16 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random problem on 2.6.12-rc1)] Grant Grundler
2005-04-09 6:00 ` David Mosberger
2005-04-22 3:50 ` [mpm@selenic.com: Re: buggy ia64_fls() ? (was Re: /dev/random Andrew Morton
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