From: Steffen Liebergeld <usenet@gmx.eu>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] Re: branches are expensive
Date: Tue, 17 Mar 2009 11:36:07 +0000 (UTC) [thread overview]
Message-ID: <gpo1v7$ddc$1@ger.gmane.org> (raw)
In-Reply-To: 49BF86FC.4060206@redhat.com
Hi Avi,
Avi Kivity <avi@redhat.com> schrieb:
> Steffen Liebergeld wrote:
>> Hi,
>>
>> while measuring the execution of an ARM guest, I encountered that branches are
>> extremely expensive in terms of executed host instructions. A single ARM
>> branch takes 148 to 152 host instructions. In my setup host and guest use the
>> ARM instruction set architecture.
>>
>> My question is what makes branches so expensive? What code is run when
>> executing a branch? Other instructions are translated to 14 to 40
>> instructions.
>>
>
> I'm no tcg guru, but if branches are not chained, you'd need an
> expensive lookup to find the next translation block. If branches are
> chained they'll probably be much faster.
Sure. But how can I get to know how many TBs are chained.
Greetings, Steffen
next prev parent reply other threads:[~2009-03-17 11:36 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-17 11:05 [Qemu-devel] branches are expensive Steffen Liebergeld
2009-03-17 11:18 ` Avi Kivity
2009-03-17 11:32 ` [Qemu-devel] " Jan Kiszka
2009-03-17 12:31 ` Steffen Liebergeld
2009-03-17 12:51 ` Paul Brook
2009-03-17 13:24 ` Avi Kivity
2009-03-19 10:07 ` Steffen Liebergeld
2009-03-19 10:30 ` Laurent Desnogues
2009-03-19 10:39 ` Steffen Liebergeld
2009-03-19 11:06 ` Laurent Desnogues
2009-03-19 10:52 ` Avi Kivity
2009-03-19 11:34 ` Paul Brook
2009-03-17 11:36 ` Steffen Liebergeld [this message]
2009-03-17 13:30 ` [Qemu-devel] " Laurent Desnogues
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