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To: Zachary Amsden <zach@vmware.com>
Cc: Linus Torvalds <torvalds@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Virtualization Mailing List <virtualization@lists.osdl.org>,
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       Pratap Subrahmanyam <pratap@vmware.com>,
       Christopher Li <chrisl@vmware.com>, Joshua LeVasseur <jtl@ira.uka.de>,
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       Wim Coekaerts <wim.coekaerts@oracle.com>,
       Leendert van Doorn <leendert@watson.ibm.com>,
       Zachary Amsden <zach@vmware.com>
Subject: Re: [RFC, PATCH 16/24] i386 Vmi io header
References: <200603131811.k2DIBS8j005741@zach-dev.vmware.com>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: Wed, 15 Mar 2006 14:17:32 -0700
In-Reply-To: <200603131811.k2DIBS8j005741@zach-dev.vmware.com> (Zachary
 Amsden's message of "Mon, 13 Mar 2006 10:11:28 -0800")
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Zachary Amsden <zach@vmware.com> writes:

> Move I/O instruction building to the sub-arch layer.  Some very crafty
> but esoteric macros are used here to get optimized native instructions
> for port I/O in Linux be writing raw instruction strings.  Adding a
> wrapper layer here is fairly easy, and makes the full range of I/O
> instructions available to the VMI interface.
>
> Also, slowing down I/O is not a useful operation in a VM, so there
> is a VMI call specifically to allow making it a NOP.  I could find
> no place where SLOW_IO_BY_JUMPING is still used, and consider it
> obsoleted.  Even on older 386 systems, the I/O delay approximation
> by touching the extra page register is likely to better.

This sounds like a prime candidate for the alternate instruction interfaces
and I don't see that being used here.

Eric
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