From: Andi Kleen <andi@firstfloor.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Liang\, Kan" <kan.liang@intel.com>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm\@vger.kernel.org" <kvm@vger.kernel.org>, "Kleen\,
Andi" <andi.kleen@intel.com>
Subject: Re: [PATCH 1/2] perf: ignore LBR and offcore_rsp.
Date: Mon, 23 Jun 2014 08:56:44 -0700 [thread overview]
Message-ID: <878uon8vr7.fsf@tassilo.jf.intel.com> (raw)
In-Reply-To: <20140623092917.GQ19860@laptop.programming.kicks-ass.net> (Peter Zijlstra's message of "Mon, 23 Jun 2014 11:29:17 +0200")
Peter Zijlstra <peterz@infradead.org> writes:
>
> So I really hate this patch, it makes the code hideous. Also, its a
> death by a thousand cuts adding endless branches in this code.
FWIW compared to the cost of a RDMSR (which is a very complex operation
for the CPU) the cost of a predicted branch is nearly in the noise.
>
> Also, the offcore part is retarded, just make sure extra_reg isn't set.
>
> As to the LBR, just make it so that we avoid calling the LBR code to
> begin with; ideally without adding extra code to fast paths.
You mean check once at initialization time.
I'm not sure that would handle all cases unfortunately.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
prev parent reply other threads:[~2014-06-23 15:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <37D7C6CF3E00A74B8858931C1DB2F0770148F513@SHSMSX103.ccr.corp.intel.com>
2014-06-18 15:59 ` [PATCH 1/2] perf: ignore LBR and offcore_rsp Peter Zijlstra
2014-06-18 16:04 ` Andi Kleen
2014-06-19 17:52 ` Andi Kleen
2014-06-23 9:19 ` Peter Zijlstra
2014-06-23 9:29 ` Peter Zijlstra
2014-06-23 15:56 ` Andi Kleen [this message]
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