From: Andrii Anisov <andrii.anisov@gmail.com>
To: Julien Grall <julien.grall@arm.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: Tue, 30 Jul 2019 20:35:21 +0300 [thread overview]
Message-ID: <63256c34-fab7-1fb8-3637-9c5a50d6d6bf@gmail.com> (raw)
In-Reply-To: <c971845f-7305-22c2-081f-9faa36e4c8d2@arm.com>
On 26.07.19 13:59, Julien Grall wrote:
> 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 ...
...In the hot path (actually at any trap).
And the function call for traps from hyp.
>> 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.
I'm not seeing any benefits in calling `enter_hypervisor_head()` from functions named `do_trap_hyp_*`. That code is confusing for me.
IMHO, dividing `do_trap_irq/fiq()` into guest and hyp specific functions is not a big deal. Even for ARM32. Moreover, it will make more obvious the fact that nothing from `enter_hypervisor_head()` is done for IRQ traps taken from hyp.
> So I am not convinced that this has any value for Xen.
OK, I wouldn't insist.
--
Sincerely,
Andrii Anisov.
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next prev parent reply other threads:[~2019-07-30 17:35 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
2019-07-30 17:35 ` Andrii Anisov [this message]
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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