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Re: [PATCH v6 03/16] libs/guest: Reduce number of I/O vectors in write_batch
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Frediano Ziglio <freddy77@xxxxxxxxx>
- Date: Thu, 2 Jul 2026 13:33:05 +0100
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>
- Delivery-date: Thu, 02 Jul 2026 12:33:22 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Tue, 30 Jun 2026 at 17:47, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
>
> This has the same exact subject as the prior patch.
>
> Either it wants merging, as they're both in the same function, or the
> subject wants to be different. Even a "Further ..." prefix would help.
>
> On 19/06/2026 2:04 pm, Frediano Ziglio wrote:
> > Each page was sent using a different iovec item. This potentially exceed
> > Linux maximum (1024).
>
> Linux cannot have a maximum of 1024 because this has been working fine
> for a decade using 1028 in the common case.
>
But the code does not call writev or similars directly, so there's no
limit besides the sky.
The result with 1028 is simply that you do 2 system calls instead of one.
> > Coalesce adjacent IO vector elements to attempt to reduce the number of
> > overall IO vectors for each operation.
> > Also some implementation (MiniOS) emulate writev with multiple write calls.
> >
> > Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
> > Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
Frediano
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