linux-kernel - Re: [Xen-devel] [PATCH RFC] p2m: use GNTTABOP_unmap_and

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Message-ID: <51FA36AC.1090609@citrix.com>
Date:	Thu, 1 Aug 2013 12:21:32 +0200
From:	Roger Pau Monné <roger.pau@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	<xen-devel@...ts.xen.org>, <linux-kernel@...r.kernel.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
Subject: Re: [Xen-devel] [PATCH RFC] p2m: use GNTTABOP_unmap_and_duplicate
 if	available

On 01/08/13 11:53, David Vrabel wrote:
> On 31/07/13 17:07, Roger Pau Monne wrote:
>> The new GNTTABOP_unmap_and_duplicate operation doesn't zero the
>> mapping passed in new_addr, allowing us to perform batch unmaps in p2m
>> code without requiring the use of a multicall.
> 
> Thanks. This looks like it should be a good performance improvement for
> userspace-based backends.  Do you have any performance measurements for
> (e.g.) qemu's disk backend?

Not yet, I might be able to get some initial performance measurements
tomorrow.

> 
>> --- a/arch/x86/xen/p2m.c
>> +++ b/arch/x86/xen/p2m.c
> [...]
>> +int m2p_remove_override_batch(struct page **pages,
>> +		struct gnttab_map_grant_ref *kmap_ops, int count)
>> +{
> 
> Is it possible to refactor this function and
> m2p_remove_override_single() to share some common helper functions?

Yes, I will split those common parts into inline functions and share
them between both implementations.

Roger.
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