From: Andy Lutomirski <luto@kernel.org>
To: Fenghua Yu <fenghua.yu@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
H Peter Anvin <hpa@zytor.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ashok Raj <ashok.raj@intel.com>,
Ravi V Shankar <ravi.v.shankar@intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [PATCH v2 2/3] x86/umwait: Setup umwait C0.2 state
Date: Wed, 16 Jan 2019 15:51:16 -0800 [thread overview]
Message-ID: <CALCETrWQMg8BEk4fZ5-GyP=VL2zEk_UQr67iQt-fqf4cC8nHcQ@mail.gmail.com> (raw)
In-Reply-To: <1547673522-226408-3-git-send-email-fenghua.yu@intel.com>
On Wed, Jan 16, 2019 at 1:24 PM Fenghua Yu <fenghua.yu@intel.com> wrote:
>
> UMWAIT or TPAUSE called by user process makes processor to reside in
> a light-weight power/performance optimized state (C0.1 state) or an
> improved power/performance optimized state (C0.2 state).
>
> IA32_UMWAIT_CONTROL MSR register allows OS to set global maximum umwait
> time and disable C0.2 on the processor.
>
> By default C0.2 is enabled so user wait instructions can enter the state
> if user wants to save more power but wakeup time is slower. In some cases
> e.g. real time, user wants to disable C0.2 and all C0.2 requests revert
> to C0.1.
>
> A new "/sys/devices/system/cpu/umwait_control/umwait_enable_c0_2" file is
> created to allow user to check if C0.2 is enabled or disabled and also
> allow user to enable or disable C0.2. Value "0" in the file means C0.2 is
> disabled. Value "1" means C0.2 is enabled.
Do you have any sense as to what the actual C0.2 entry and exit latency is?
--Andy
next prev parent reply other threads:[~2019-01-16 23:51 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-16 21:18 [PATCH v2 0/3] x86/umwait: Enable user wait instructions Fenghua Yu
2019-01-16 21:18 ` [PATCH v2 1/3] x86/cpufeatures: Enumerate " Fenghua Yu
2019-01-16 21:18 ` [PATCH v2 2/3] x86/umwait: Setup umwait C0.2 state Fenghua Yu
2019-01-16 23:51 ` Andy Lutomirski [this message]
2019-01-16 21:18 ` [PATCH v2 3/3] x86/umwait: Control umwait maximum time Fenghua Yu
2019-01-17 0:00 ` Andy Lutomirski
2019-01-17 0:07 ` Fenghua Yu
2019-01-17 0:30 ` Andy Lutomirski
2019-01-17 2:06 ` Fenghua Yu
2019-01-20 19:12 ` Andrew Cooper
2019-01-20 21:40 ` Andy Lutomirski
2019-02-08 18:51 ` Yu, Fenghua
2019-01-16 21:18 ` [PATCH v2 0/3] x86/umwait: Enable user wait instructions Fenghua Yu
2019-01-16 21:18 ` [PATCH v2 1/3] x86/cpufeatures: Enumerate " Fenghua Yu
2019-02-21 6:37 ` Andy Lutomirski
2019-02-21 9:22 ` Peter Zijlstra
2019-02-21 19:24 ` Fenghua Yu
2019-02-21 22:57 ` Yu, Fenghua
2019-02-24 19:45 ` Andy Lutomirski
2019-02-26 19:53 ` Fenghua Yu
2019-02-22 2:09 ` Tao Xu
2019-02-26 20:41 ` Fenghua Yu
2019-01-16 21:18 ` [PATCH v2 2/3] x86/umwait: Setup umwait C0.2 state Fenghua Yu
2019-01-16 21:18 ` [PATCH v2 3/3] x86/umwait: Control umwait maximum time Fenghua Yu
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