> -----Original Message----- > From: Julien Grall <jul...@xen.org> > Sent: 16 September 2020 09:39 > To: p...@xen.org; 'Jan Beulich' <jbeul...@suse.com>; 'Oleksandr Tyshchenko' > <olekst...@gmail.com> > Cc: xen-devel@lists.xenproject.org; 'Oleksandr Tyshchenko' > <oleksandr_tyshche...@epam.com>; 'Stefano > Stabellini' <sstabell...@kernel.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 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
If that happens then we'll probably want to move (back to) a list rather than an array... > > > 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. > ... which will seamlessly deal with this issue. Paul > Cheers, > > -- > Julien Grall
