From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH 1/4] Pte drop ptep_get_and_clear paravirt op.patch
Date: Tue, 17 Apr 2007 09:32:44 -0400
Message-ID: <4624CC7C.6040107@goop.org>
References: <200704120530.l3C5Ubs0022821@zach-dev.vmware.com>
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To: Zachary Amsden <zach@vmware.com>
Cc: Andrew Morton <akpm@osdl.org>, Andi Kleen <ak@muc.de>, Rusty Russell <rusty@rustcorp.com.au>, Chris Wright <chrisw@sous-sol.org>, Hugh Dickins <hugh@veritas.com>, David Rientjes <rientjes@google.com>, Michel Lespinasse <walken@vmware.com>, Virtualization Mailing List <virtualization@lists.osdl.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
List-Id: virtualization@lists.linuxfoundation.org

Zachary Amsden wrote:
> In shadow mode hypervisors, ptep_get_and_clear achieves the desired
> purpose of keeping the shadows in sync by issuing a native_get_and_clear,
> followed by a call to pte_update, which indicates the PTE has been
> modified.
>
> Direct mode hypervisors (Xen) have no need for this anyway, and will trap
> the update using writable pagetables.
>   

Jan Beulich just posted a patch for Xen/linux which specialzes
ptep_get_and_clear, which apparently improves kernel-compile performance
by 25-30% on some configurations.  I think we'll want to keep this.

    J