Re: [PATCH v5 2/2] x86, mwaitt: introduce mwaix delay with a configurable timer

From: Huang Rui <ray.huang@amd.com>
To: Borislav Petkov <bp@suse.de>
Cc: "Peter Zijlstra" <peterz@infradead.org>,
	"Andy Lutomirski" <luto@amacapital.net>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	"Len Brown" <lenb@kernel.org>,
	"John Stultz" <john.stultz@linaro.org>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	"Fengguang Wu" <fengguang.wu@intel.com>,
	"Aaron Lu" <aaron.lu@intel.com>,
	"Suravee Suthikulanit" <suravee.suthikulpanit@amd.com>,
	"Tony Li" <tony.li@amd.com>, "Ken Xue" <ken.xue@amd.com>
Subject: Re: [PATCH v5 2/2] x86, mwaitt: introduce mwaix delay with a configurable timer
Date: Mon, 15 Jun 2015 22:04:19 +0800	[thread overview]
Message-ID: <20150615140418.GB28310@hr-slim.amd.com> (raw)
In-Reply-To: <20150615111526.GB4481@pd.tnic>

On Mon, Jun 15, 2015 at 01:15:26PM +0200, Borislav Petkov wrote:
> On Mon, Jun 15, 2015 at 12:57:18PM +0200, Peter Zijlstra wrote:
> > Seeing how we disable C states, its unlikely to use less energy, so what
> > exactly is its benefit, other than using fancy new instructions?
> 
> If the "disabling of C states" turns into a "go into a C-state which has
> small wakeup latency" in the future, would be cool. Because we have a
> bunch of places where we do delay.
> 
> Rui, what happens if you enter C1 instead? Any improvements or is the
> wakeup latency too high?
> 

Hmm, the current processor cannot enter C1 with MWAITX, so I don't
confirm if it would have higher wakeup latency on C1 in future.

Thanks,
Rui