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From: Julien Grall <julien.grall@arm.com>
To: Andrii Anisov <andrii.anisov@gmail.com>, xen-devel@lists.xenproject.org
Cc: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Andrii Anisov <andrii_anisov@epam.com>
Subject: Re: [Xen-devel] [RFC 5/6] arm64: call enter_hypervisor_head only when it is needed
Date: Fri, 26 Jul 2019 11:59:54 +0100	[thread overview]
Message-ID: <c971845f-7305-22c2-081f-9faa36e4c8d2@arm.com> (raw)
In-Reply-To: <1564137460-25629-7-git-send-email-andrii.anisov@gmail.com>

Hi,

On 26/07/2019 11:37, Andrii Anisov wrote:
> From: Andrii Anisov <andrii_anisov@epam.com>
> 
> On ARM64 we know exactly if trap happened from hypervisor or guest, so
> we do not need to take that decision. This reduces a condition for
> all enter_hypervisor_head calls and the function call for traps from
> the hypervisor mode.

One condition lost but ...

> 
> Currently, it is implemented for ARM64 only. Integrating the stuff
> with ARM32 requires moving ` if ( guest_mode(regs) )` condition
> into ARM32 specific traps.

... one more divergence between arm32 and arm64.

There are probably dozens of more conditions in the code that are not necessary 
for one of the architectures. Yet there are value to keep everything common 
because the benefits outweigh the likely non performance improvement.

So I am not convinced that this has any value for Xen.

Cheers,

-- 
Julien Grall

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  reply	other threads:[~2019-07-26 11:00 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-26 10:37 [Xen-devel] [RFC 0/6] XEN scheduling hardening Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 1/6] xen/arm: Re-enable interrupt later in the trap path Andrii Anisov
2019-07-26 10:48   ` Julien Grall
2019-07-30 17:35     ` Andrii Anisov
2019-07-30 20:10       ` Julien Grall
2019-08-01  6:45         ` Andrii Anisov
2019-08-01  9:37           ` Julien Grall
2019-08-02  8:28             ` Andrii Anisov
2019-08-02  9:03               ` Julien Grall
2019-08-02 12:24                 ` Andrii Anisov
2019-08-02 13:22                   ` Julien Grall
2019-08-01 11:19           ` Dario Faggioli
2019-08-02  7:50             ` Andrii Anisov
2019-08-02  9:15               ` Julien Grall
2019-08-02 13:07                 ` Andrii Anisov
2019-08-02 13:49                   ` Julien Grall
2019-08-03  1:39                     ` Dario Faggioli
2019-08-03  0:55                   ` Dario Faggioli
2019-08-06 13:09                     ` Andrii Anisov
2019-08-08 14:07                       ` Andrii Anisov
2019-08-13 14:45                         ` Dario Faggioli
2019-08-15 18:25                           ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 2/6] schedule: account true system idle time Andrii Anisov
2019-07-26 12:00   ` Dario Faggioli
2019-07-26 12:42     ` Andrii Anisov
2019-07-29 11:40       ` Dario Faggioli
2019-08-01  8:23         ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 3/6] sysctl: extend XEN_SYSCTL_getcpuinfo interface Andrii Anisov
2019-07-26 12:15   ` Dario Faggioli
2019-07-26 13:06     ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 4/6] xentop: show CPU load information Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 5/6] arm64: сall enter_hypervisor_head only when it is needed Andrii Anisov
2019-07-26 10:44   ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 5/6] arm64: call " Andrii Anisov
2019-07-26 10:59   ` Julien Grall [this message]
2019-07-30 17:35     ` Andrii Anisov
2019-07-31 11:02       ` Julien Grall
2019-07-31 11:33         ` Andre Przywara
2019-08-01  7:33         ` Andrii Anisov
2019-08-01 10:17           ` Julien Grall
2019-08-02 13:50             ` Andrii Anisov
2019-07-26 10:37 ` [Xen-devel] [RFC 6/6] schedule: account all the hypervisor time to the idle vcpu Andrii Anisov
2019-07-26 11:56 ` [Xen-devel] [RFC 0/6] XEN scheduling hardening Dario Faggioli
2019-07-26 12:14   ` Juergen Gross
2019-07-29 11:53     ` Dario Faggioli
2019-07-29 12:13       ` Juergen Gross
2019-07-29 14:47     ` Andrii Anisov
2019-07-29 18:46       ` Dario Faggioli
2019-07-29 14:28   ` Andrii Anisov

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