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From: Len Brown <lenb@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>,
	"Chang S. Bae" <chang.seok.bae@intel.com>,
	Borislav Petkov <bp@suse.de>, Ingo Molnar <mingo@kernel.org>,
	X86 ML <x86@kernel.org>, "Brown, Len" <len.brown@intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	"Liu, Jing2" <jing2.liu@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Documentation List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v4 22/22] x86/fpu/xstate: Introduce boot-parameters to control state component support
Date: Mon, 29 Mar 2021 09:31:27 -0400	[thread overview]
Message-ID: <CAJvTdKkOED6p0ox83A0qcspi5UZ-UbZAkJeyOJ6AChb-qnZGwQ@mail.gmail.com> (raw)
In-Reply-To: <87r1k0ck7o.ffs@nanos.tec.linutronix.de>

On Sat, Mar 27, 2021 at 6:20 PM Thomas Gleixner <tglx@linutronix.de> wrote:

> What's the actual downside of issuing TILERELEASE conditionally
> depending on prev->AMX INIT=0? Is it slooooow or what's the real
> problem here?

TILERELEASE is fast, so there should be no down-side to execute it.
Indeed, checking whether you need to execute it or not will probably take
longer than executing TILERELEASE.  My point (perhaps academic)
is that Linux should not have to know about TILERELEASE, or execute it.

Re: running in the kernel with AMX INIT=0

AMX INIT=0 will prevent c6 on that core.  I don't expect to see this
in the syscall path, though if a user wanted to neglect to issue TILERELEASE,
there is nothing forcing them to do so.

It can certainly happen on the interrupt path, but on the interrupt patch
I don't know if we can end up requesting c6 -- perhaps on a forced
task migration?

Re:  frequency credits in the kernel with AMX INIT=0.

It works exactly the same way as AMX INIT=1.
That is to say, the frequency credits don't key off of AMX INIT,
they key off of the actual use of the AMX execution unit, and
the credits free up several orders of magnitude faster
(both for AVX-512 and AMX) on this hardware as in previous generations.

As a result, if we interrupt an AMX program, and run for an extended
period of time in the kernel without XRESTOR to clear out his AMX INIT=0 state,
that will not have any impact on the frequency we run inside the kernel any more
than if he had AMX INIT=1 state.

thanks,
Len Brown, Intel Open Source Technology Center

  reply	other threads:[~2021-03-29 13:32 UTC|newest]

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-21 18:56 [PATCH v4 00/22] x86: Support Intel Advanced Matrix Extensions Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 01/22] x86/fpu/xstate: Modify the initialization helper to handle both static and dynamic buffers Chang S. Bae
2021-03-10 13:40   ` Borislav Petkov
2021-02-21 18:56 ` [PATCH v4 02/22] x86/fpu/xstate: Modify state copy helpers " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 03/22] x86/fpu/xstate: Modify address finders " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 04/22] x86/fpu/xstate: Modify the context restore helper " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 05/22] x86/fpu/xstate: Add a new variable to indicate dynamic user states Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 06/22] x86/fpu/xstate: Add new variables to indicate dynamic xstate buffer size Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 07/22] x86/fpu/xstate: Calculate and remember dynamic xstate buffer sizes Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 08/22] x86/fpu/xstate: Convert the struct fpu 'state' field to a pointer Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 09/22] x86/fpu/xstate: Introduce helpers to manage the xstate buffer dynamically Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 10/22] x86/fpu/xstate: Define the scope of the initial xstate data Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 11/22] x86/fpu/xstate: Update the xstate save function to support dynamic states Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 12/22] x86/fpu/xstate: Update the xstate buffer address finder " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 13/22] x86/fpu/xstate: Update the xstate context copy function " Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the first use of dynamic user state Chang S. Bae
2021-03-20 22:13   ` Thomas Gleixner
2021-03-20 22:21     ` Andy Lutomirski
2021-03-23 21:01       ` Len Brown
2021-03-24  3:14         ` Liu, Jing2
2021-03-24 21:09           ` Len Brown
2021-03-24 21:26             ` Andy Lutomirski
2021-03-24 21:30               ` Dave Hansen
2021-03-24 21:42                 ` Andy Lutomirski
2021-03-24 21:58                   ` Dave Hansen
2021-03-24 22:12                     ` Andy Lutomirski
2021-03-25  5:12             ` Liu, Jing2
2021-03-25  6:59               ` Bae, Chang Seok
2021-03-25  7:26                 ` Liu, Jing2
2021-03-23 21:52     ` Bae, Chang Seok
2021-03-24 14:24       ` Dave Hansen
2021-03-29 13:14     ` Len Brown
2021-03-29 13:33       ` Thomas Gleixner
2021-03-29 15:43         ` Len Brown
2021-03-29 16:06           ` Len Brown
2021-03-29 17:43             ` Andy Lutomirski
2021-03-29 18:57               ` Len Brown
2021-03-29 18:49           ` Thomas Gleixner
2021-03-29 22:16             ` Len Brown
2021-03-30  8:28               ` Thomas Gleixner
2021-03-30 16:38                 ` Len Brown
2021-03-26 16:34   ` Jann Horn
2021-03-29 18:14     ` Bae, Chang Seok
2021-02-21 18:56 ` [PATCH v4 15/22] x86/fpu/xstate: Support ptracer-induced xstate buffer expansion Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 16/22] x86/fpu/xstate: Extend the table to map state components with features Chang S. Bae
2021-03-20 21:25   ` Thomas Gleixner
2021-03-23 21:52     ` Bae, Chang Seok
2021-02-21 18:56 ` [PATCH v4 17/22] x86/cpufeatures/amx: Enumerate Advanced Matrix Extension (AMX) feature bits Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 18/22] x86/fpu/amx: Define AMX state components and have it used for boot-time checks Chang S. Bae
2021-03-20 21:31   ` Thomas Gleixner
2021-03-23 21:52     ` Bae, Chang Seok
2021-02-21 18:56 ` [PATCH v4 19/22] x86/fpu/amx: Enable the AMX feature in 64-bit mode Chang S. Bae
2021-03-20 21:26   ` Thomas Gleixner
2021-03-23 21:51     ` Bae, Chang Seok
2021-02-21 18:56 ` [PATCH v4 20/22] selftest/x86/amx: Include test cases for the AMX state management Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 21/22] x86/fpu/xstate: Support dynamic user state in the signal handling path Chang S. Bae
2021-02-21 18:56 ` [PATCH v4 22/22] x86/fpu/xstate: Introduce boot-parameters to control state component support Chang S. Bae
2021-02-21 19:30   ` Randy Dunlap
2021-02-21 20:10     ` Bae, Chang Seok
2021-02-21 20:37       ` Randy Dunlap
2021-03-20 20:56   ` Thomas Gleixner
2021-03-25 22:59     ` Len Brown
2021-03-25 23:10       ` Dave Hansen
2021-03-26 15:27         ` Len Brown
2021-03-26 19:22           ` Thomas Gleixner
2021-03-26  1:41       ` Andy Lutomirski
2021-03-26 15:33         ` Len Brown
2021-03-26 15:48           ` Andy Lutomirski
2021-03-26 17:53             ` Len Brown
2021-03-26 18:12               ` Andy Lutomirski
2021-03-27  4:53                 ` Len Brown
2021-03-27 22:20                   ` Thomas Gleixner
2021-03-29 13:31                     ` Len Brown [this message]
2021-03-29 14:10                       ` Thomas Gleixner
2021-03-26 18:17               ` Borislav Petkov
2021-03-27  4:41                 ` Len Brown
2021-03-26  1:50       ` Thomas Gleixner
2021-03-26 15:36         ` Len Brown

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