linux-kernel - Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors based on the Zen microarchitecture

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YywaAcTdLSuDlRfl@hirez.programming.kicks-ass.net>
Date:   Thu, 22 Sep 2022 10:17:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     K Prateek Nayak <kprateek.nayak@....com>,
        linux-kernel@...r.kernel.org, rafael@...nel.org, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
        dave.hansen@...ux.intel.com, tglx@...utronix.de, andi@...as.de,
        puwen@...on.cn, mario.limonciello@....com, rui.zhang@...el.com,
        gpiccoli@...lia.com, daniel.lezcano@...aro.org,
        ananth.narayan@....com, gautham.shenoy@....com,
        Calvin Ong <calvin.ong@....com>, stable@...r.kernel.org,
        regressions@...ts.linux.dev
Subject: Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors
 based on the Zen microarchitecture

On Wed, Sep 21, 2022 at 09:48:13PM +0200, Borislav Petkov wrote:
> On Wed, Sep 21, 2022 at 05:00:35PM +0200, Peter Zijlstra wrote:
> > On Wed, Sep 21, 2022 at 12:06:38PM +0530, K Prateek Nayak wrote:
> > > Processors based on the Zen microarchitecture support IOPORT based deeper
> > > C-states. 
> > 
> > I've just gotta ask; why the heck are you using IO port based idle
> > states in 2022 ?!?! You have have MWAIT, right?
> 
> They have both. And both is Intel technology. And as I'm sure you
> know AMD can't do their own thing - they kinda have to follow Intel.
> Unfortunately.
> 
> Are you saying modern Intel chipsets don't do IO-based C-states anymore?

I've no idea what they do, but Linux exclusively uses MWAIT on Intel as
per intel_idle.c.

MWAIT also cuts down on IPIs because it wakes from the TIF write.