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Subject: Re: [Qemu-devel] [PATCH v2] xen_disk: add persistent grant support
 to xen_disk backend
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Anthony Perard <anthony.perard@citrix.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>

On 09/01/13 13:48, Stefano Stabellini wrote:
> On Tue, 8 Jan 2013, Roger Pau Monne wrote:
>> This protocol extension reuses the same set of grant pages for all
>> transactions between the front/back drivers, avoiding expensive tlb
>> flushes, grant table lock contention and switches between userspace
>> and kernel space. The full description of the protocol can be found in
>> the public blkif.h header.
>>
>> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob_plain;f=xen/include/public/io/blkif.h
>>
>> Speed improvement with 15 guests performing I/O is ~450%.
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
>> Cc: xen-devel@lists.xen.org
>> Cc: Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>
>> Cc: Anthony PERARD <anthony.perard@citrix.com>
>> ---
>> Performance comparison with the previous implementation can be seen in
>> the followign graph:
>>
>> http://xenbits.xen.org/people/royger/persistent_read_qemu.png
>> ---
>> Changes since v1:
>>  * Fix coding style issues.
>>  * Add more comments regarding how ioreq_map works.
> 
> The patch looks good now, I only have a very small stylistic comment.
> 
> 
>> +    for (i = 0; i < ioreq->v.niov; i++) {
>> +        ioreq->v.iov[i].iov_base = page[i] +
>> +                                   (uintptr_t)ioreq->v.iov[i].iov_base;
> 
> ioreq->v.iov[i].iov_base += (uintptr_t)page[i] ?

True. Would you like to fix that yourself before committing, or do you
want me to resend?

Thanks for the review.