From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: linux-kernel@vger.kernel.org, npiggin@gmail.com,
Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/bug: Remove specific powerpc BUG_ON()
Date: Thu, 11 Feb 2021 06:39:07 -0600 [thread overview]
Message-ID: <20210211123907.GD28121@gate.crashing.org> (raw)
In-Reply-To: <3b7f3a1e-0355-b6d4-14cd-300bf4d3629a@csgroup.eu>
On Thu, Feb 11, 2021 at 01:26:12PM +0100, Christophe Leroy wrote:
> >What PowerPC cpus implement branch folding? I know none.
>
> Extract from powerpc mpc8323 reference manual:
> — Zero-cycle branch capability (branch folding)
Yeah, this is not what is traditionally called branch folding (which
stores the instruction being branched to in some cache, originally the
instruction cache itself; somewhat similar (but different) to the BTIC
on 750). Overloaded terminology :-)
6xx/7xx CPUs had the branch execution unit in the frontend, and it would
not issue a branch at all if it could be resolved then already. Power4
and later predict all branches, and most are not issued at all (those
that do need to be executed, like bdnz, are). At completion time it is
checked if the prediction was correct (and corrective action is taken if
not).
Segher
next prev parent reply other threads:[~2021-02-11 12:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-11 7:41 [PATCH] powerpc/bug: Remove specific powerpc BUG_ON() Christophe Leroy
2021-02-11 10:04 ` Nicholas Piggin
2021-02-11 11:50 ` Segher Boessenkool
2021-02-11 22:47 ` Nicholas Piggin
2021-02-11 12:22 ` Segher Boessenkool
2021-02-11 11:49 ` Segher Boessenkool
2021-02-11 12:26 ` Christophe Leroy
2021-02-11 12:39 ` Segher Boessenkool [this message]
2021-02-11 14:09 ` Christophe Leroy
2021-02-11 14:30 ` Segher Boessenkool
2021-02-11 15:30 ` Christophe Leroy
2021-02-27 10:31 ` Christophe Leroy
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