From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH 1/3] x86: Move msr accesses out of line
Date: Mon, 23 Feb 2015 18:04:36 +0100 [thread overview]
Message-ID: <20150223170436.GC5029@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1424482737-958-1-git-send-email-andi@firstfloor.org>
On Fri, Feb 20, 2015 at 05:38:55PM -0800, Andi Kleen wrote:
> This patch moves the MSR functions out of line. A MSR access is typically
> 40-100 cycles or even slower, a call is a few cycles at best, so the
> additional function call is not really significant.
If I look at the below PDF a CALL+PUSH EBP+MOV RSP,RBP+ ... +POP+RET
ends up being 5+1.5+0.5+ .. + 1.5+8 = 16.5 + .. cycles.
~16 is fairly significant on 40. And I figure people are working hard to
make some MSR accesses cheaper, which means it'll be even worse in the
future.
Now I appreciate the intent for debuggability, but I don't think we can
do this unconditionally.
http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-optimization-manual.html
next prev parent reply other threads:[~2015-02-23 17:04 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-21 1:38 [PATCH 1/3] x86: Move msr accesses out of line Andi Kleen
2015-02-21 1:38 ` [PATCH 2/3] x86: Add trace point for MSR accesses Andi Kleen
2015-02-21 1:38 ` [PATCH 3/3] perf, x86: Remove old MSR perf tracing code Andi Kleen
2015-02-23 17:04 ` Peter Zijlstra [this message]
2015-02-23 17:43 ` [PATCH 1/3] x86: Move msr accesses out of line Andi Kleen
2015-02-25 12:27 ` Peter Zijlstra
2015-02-25 18:20 ` Andi Kleen
2015-02-25 18:34 ` Borislav Petkov
2015-02-26 11:43 ` [RFC][PATCH] module: Optimize __module_address() using a latched RB-tree Peter Zijlstra
2015-02-26 12:00 ` Ingo Molnar
2015-02-26 14:12 ` Peter Zijlstra
2015-02-27 11:51 ` Rusty Russell
2015-02-26 16:02 ` Mathieu Desnoyers
2015-02-26 16:43 ` Peter Zijlstra
2015-02-26 16:55 ` Mathieu Desnoyers
2015-02-26 17:16 ` Peter Zijlstra
2015-02-26 17:22 ` Peter Zijlstra
2015-02-26 18:28 ` Paul E. McKenney
2015-02-26 19:06 ` Mathieu Desnoyers
2015-02-26 19:13 ` Peter Zijlstra
2015-02-26 19:41 ` Paul E. McKenney
2015-02-26 19:45 ` Peter Zijlstra
2015-02-26 22:32 ` Peter Zijlstra
2015-02-26 20:52 ` Andi Kleen
2015-02-26 22:36 ` Peter Zijlstra
2015-02-27 10:01 ` Peter Zijlstra
2015-02-28 23:30 ` Paul E. McKenney
2015-02-28 16:41 ` Peter Zijlstra
2015-02-28 16:56 ` Peter Zijlstra
2015-02-28 23:32 ` Paul E. McKenney
2015-03-02 9:24 ` Peter Zijlstra
2015-03-02 16:58 ` Paul E. McKenney
2015-02-27 12:02 ` Rusty Russell
2015-02-27 14:30 ` Peter Zijlstra
-- strict thread matches above, loose matches on Subject: below --
2015-03-20 0:29 Updated MSR tracing patchkit v2 Andi Kleen
2015-03-20 0:29 ` [PATCH 1/3] x86: Move msr accesses out of line Andi Kleen
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