From: "Yin, Fengwei" <fengwei.yin@intel.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Len Brown <lenb@kernel.org>,
"open list:ACPI" <linux-acpi@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [RESEND] ACPI / processor_idle: use dead loop instead of io port access for wait
Date: Mon, 14 Oct 2019 17:54:47 +0800 [thread overview]
Message-ID: <6b8a0f55-67f7-98b1-c252-301628f9d5e2@intel.com> (raw)
In-Reply-To: <3727681.FYoUZqeJdN@kreacher>
On 10/14/2019 5:38 PM, Rafael J. Wysocki wrote:
> On Friday, October 11, 2019 3:30:41 PM CEST Yin, Fengwei wrote:
>>
>> On 10/11/2019 5:05 PM, Rafael J. Wysocki wrote:
>>> Sorry for the delay.
>> No problem.
>>
>>>
>>> On Monday, September 9, 2019 9:39:37 AM CEST Yin Fengwei wrote:
>>>> In function acpi_idle_do_entry(), we do an io port access to guarantee
>>>> hardware behavior. But it could trigger unnecessary vmexit for
>>>> virtualization environemnt.
>>>
>>> Is this a theoretical problem, or do you actually see it?
>>>
>>> If you see it, I'd like to have a pointer to a bug report regarding it
>>> or similar.
>> We did see this issue when we run linux as guest with ACRN hypervisor
>> instead of kvm or xen. In our case, we export all native C states to
>> guest and let guest choose which C state it will enter.
>>
>> And we observed many pm timer port access when guest tried to enter
>> deeper C state (Yes, we emulate pm timer so pm timer access will trigger
>> vmexit).
>
> Can you please put this information into the changelog of your patch?
Sure. Just want to double confirm into changelog or commit message?
Regards
Yin, Fengwei
>
> It works very well as a rationale for me. :-)
>
>
>
next prev parent reply other threads:[~2019-10-14 9:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-09 7:39 [RESEND] ACPI / processor_idle: use dead loop instead of io port access for wait Yin Fengwei
2019-10-11 9:05 ` Rafael J. Wysocki
2019-10-11 13:30 ` Yin, Fengwei
2019-10-14 9:38 ` Rafael J. Wysocki
2019-10-14 9:54 ` Yin, Fengwei [this message]
2019-10-15 8:03 ` Yin, Fengwei
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