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From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: The killing of ideal_nops[]
Date: Wed, 10 Mar 2021 09:13:24 -0500	[thread overview]
Message-ID: <20210310091324.0c346d5f@oasis.local.home> (raw)
In-Reply-To: <YEid+HQnqgnt3iyY@hirez.programming.kicks-ass.net>

On Wed, 10 Mar 2021 11:22:48 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> After this FEATURE_NOPL is unused except for required-features for
> x86_64. FEATURE_K8 is only used for PTI and FEATURE_K7 is unused.
> 
> AFAICT this negatively affects lots of 32bit (DONTCARE) and 32bit on
> 64bit CPUs (CARELESS) and early AMD (K8) which is from 2003 and almost
> 2 decades old by now (SHRUG).
> 
> Everything x86_64 since AMD K10 (2007) was using p6_nops.
> 
> And per FEATURE_NOPL being required for x86_64, all those CPUs can use
> p6_nops. So stop caring about NOPs, simplify things and get on with life
> :-)

Before ripping out all the ideal_nop logic, I wonder if we should just
force the nops you want now (that is, don't change the selected
ideal_nops, just "pretend" that the CPU wants p6_nops), and see if anyone
complains. After a few releases, if there's no complaints, then we can
rip out the ideal_nop logic.

-- Steve

  reply	other threads:[~2021-03-10 14:14 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-09 16:58 The killing of ideal_nops[] Peter Zijlstra
2021-03-09 17:05 ` Steven Rostedt
2021-03-09 21:24   ` Peter Zijlstra
2021-03-10  0:33     ` hpa
2021-03-10  9:14       ` Peter Zijlstra
2021-03-10  9:35         ` Peter Zijlstra
2021-03-10 10:03           ` Peter Zijlstra
2021-03-10 10:22             ` Peter Zijlstra
2021-03-10 14:13               ` Steven Rostedt [this message]
2021-03-10 14:24                 ` Peter Zijlstra
2021-03-10 14:30                   ` Peter Zijlstra
2021-03-10 15:48                   ` Alexei Starovoitov
2021-03-10 16:04                     ` Peter Zijlstra
2021-03-11  9:28                       ` David Laight
2021-03-14 22:43                       ` Maciej W. Rozycki

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