From: Borislav Petkov <bp@alien8.de>
To: "Ghannam, Yazen" <Yazen.Ghannam@amd.com>
Cc: "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"rjw@rjwysocki.net" <rjw@rjwysocki.net>,
"len.brown@intel.com" <len.brown@intel.com>,
"pavel@ucw.cz" <pavel@ucw.cz>
Subject: Re: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD systems
Date: Tue, 23 May 2017 09:59:11 +0200 [thread overview]
Message-ID: <20170523075911.GA25383@nazgul.tnic> (raw)
In-Reply-To: <BN6PR1201MB01312A2AB93708B9115D4865F8F80@BN6PR1201MB0131.namprd12.prod.outlook.com>
On Mon, May 22, 2017 at 08:20:56PM +0000, Ghannam, Yazen wrote:
> On the other hand, MWAIT on AMD limits the hardware to using only certain,
> shallower Cstates. This is okay if we define individual states and use MWAIT
> for some of them. But it would consume more power if used always.
Let me see if I understand it correctly:
Even though we used to do HLT on previous families as idling with HLT
*is* the preferred method until now, with your change you're moving
*every* AMD machine out there to do MWAIT now.
Lemme look at the F15h BKDG:
"2.5.3.2
C-state Request Interface
C-states are dynamically requested by software and are exposed through
ACPI objects (see 2.5.3.6 [ACPI Processor C-state Objects]). C-states
can be requested on a per-core basis. Software requests a C-state change
in one of two ways, either by executing the HLT instruction or by
reading from an IO address specified by MSRC001_0073[CstateAddr] plus an
offset of 0 through 7 (see D18F4x11[C:8])."
So this doesn't say anything about using MWAIT.
What's up?
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
next prev parent reply other threads:[~2017-05-23 7:59 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-17 14:20 [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD systems Yazen Ghannam
2017-05-22 16:21 ` Borislav Petkov
2017-05-22 20:20 ` Ghannam, Yazen
2017-05-23 7:59 ` Borislav Petkov [this message]
2017-05-23 12:50 ` Ghannam, Yazen
2017-05-23 13:06 ` Borislav Petkov
2017-05-23 12:24 ` Pavel Machek
2017-05-24 18:16 ` Ghannam, Yazen
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