On 16/09/2020 09:13, Paul Durrant wrote:
-----Original Message-----
From: Jan Beulich <[email protected]>
Sent: 16 September 2020 09:05
To: Oleksandr Tyshchenko <[email protected]>; Paul Durrant <[email protected]>
Cc: [email protected]; Oleksandr Tyshchenko
<[email protected]>; Stefano
Stabellini <[email protected]>; Julien Grall <[email protected]>; Volodymyr
Babchuk
<[email protected]>; Andrew Cooper <[email protected]>; Wei Liu
<[email protected]>; Roger
Pau Monné <[email protected]>; Julien Grall <[email protected]>
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 <[email protected]>
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
