linux-kernel - Re: [PATCH v2 1/4] x86, mwaitt: add monitorx and mwaitx instruction

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]

Date:	Tue, 9 Jun 2015 19:06:14 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"Xue, Ken" <Ken.Xue@....com>, Thomas Gleixner <tglx@...utronix.de>,
	"Li, Tony" <Tony.Li@....com>, "x86@...nel.org" <x86@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Aaron Lu <aaron.lu@...el.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Len Brown <lenb@...nel.org>, Huang Rui <ray.huang@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 1/4] x86, mwaitt: add monitorx and mwaitx instruction

On Tue, Jun 09, 2015 at 09:44:59AM -0700, Andy Lutomirski wrote:
> [1] For those who weren't bitten by this repeatedly, modern Intel CPUs
> (at least Sandy Bridge, anyway) will, by default, detect when all
> cores are in C1 or deeper, think to themselves "wow, the OS selected
> C1 -- it must want a very deep sleep indeed", and put the whole
> package into some kind of deep sleep state.  The subsequent wakeup
> takes tens of milliseconds.  Doing this in udelay would be awful.

That's a good point. Reportedly, the current MWAITX enters something
between C0 and C1 but the way I understood it, going forward, it will
enter deeper sleep states.

So for shallow C-states, your idle enter/exit latency is low enough but
I'd guess deeper states would be a problem.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/