On 16/09/2020 09:13, Paul Durrant wrote:
-----Original Message-----
From: Jan Beulich <jbeul...@suse.com>
Sent: 16 September 2020 09:05
To: Oleksandr Tyshchenko <olekst...@gmail.com>; Paul Durrant <p...@xen.org>
Cc: xen-devel@lists.xenproject.org; Oleksandr Tyshchenko
<oleksandr_tyshche...@epam.com>; Stefano
Stabellini <sstabell...@kernel.org>; Julien Grall <jul...@xen.org>; Volodymyr
Babchuk
<volodymyr_babc...@epam.com>; Andrew Cooper <andrew.coop...@citrix.com>; Wei Liu
<w...@xen.org>; Roger
Pau Monné <roger....@citrix.com>; Julien Grall <julien.gr...@arm.com>
Subject: Re: [PATCH V1 11/16] xen/ioreq: Introduce hvm_domain_has_ioreq_server()
On 10.09.2020 22:22, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshche...@epam.com>
This patch introduces a helper the main purpose of which is to check
if a domain is using IOREQ server(s).
On Arm the benefit is to avoid calling handle_hvm_io_completion()
(which implies iterating over all possible IOREQ servers anyway)
on every return in leave_hypervisor_to_guest() if there is no active
servers for the particular domain.
Is this really worth it? The limit on the number of ioreq serves is small... just 8.
When I suggested this, I failed to realize there was only 8 IOREQ
servers available. However, I would not be surprised if this increase
long term as we want to use
I doubt you'd be able measure the difference.
Bear in mind that entry/exit to the hypervisor is pretty "cheap" on Arm
compare to x86. So we want to avoid doing extra work if it is not necessary.
Cheers,
--
Julien Grall
