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From: Thomas Gleixner <tglx@linutronix.de>
To: Fenghua Yu <fenghua.yu@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, H Peter Anvin <hpa@zytor.com>,
	Ashok Raj <ashok.raj@intel.com>, Alan Cox <alan@linux.intel.com>,
	Ravi V Shankar <ravi.v.shankar@intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [RFC PATCH 1/8] x86/cpufeatures: Enumerate MOVDIRI instruction
Date: Wed, 20 Jun 2018 00:32:14 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1806200031370.10546@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180619213644.GC112652@romley-ivt3.sc.intel.com>

On Tue, 19 Jun 2018, Fenghua Yu wrote:

> On Tue, Jun 19, 2018 at 10:57:44AM +0200, Thomas Gleixner wrote:
> > On Fri, 15 Jun 2018, Fenghua Yu wrote:
> > 
> > > MOVDIRI moves doubleword or quadword from register to memory through
> > > direct store which is implemented by using write combining (WC) for
> > > writing data directly into memory without caching the data.
> > 
> > And that is useful for what?
> 
> Programmable agents can handle streaming offload (e.g. high speed packet
> processing in network). Hardware implements a doorbell (tail pointer)
> register that is updated by software when adding new work-elements to
> the streaming offload work-queue.
> 
> MOVDIRI can be used as the doorbell write which is a 4-byte or 8-byte
> uncachable write to MMIO. MOVDIRI has lower overhead than other ways
> to write the doorbell.
> 
> In low latency offload (e.g. Non-Volatile Memory, etc), MOVDIR64B writes
> work descriptors (and data in some cases) to device-hosted work-queues
> with atomicity.

Makes sense, but why is this not part of the changelog ?

Thanks,

	tglx

  reply	other threads:[~2018-06-19 22:32 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-16  3:06 [RFC PATCH 0/8] x86: Enable a few new instructions Fenghua Yu
2018-06-16  3:06 ` [RFC PATCH 1/8] x86/cpufeatures: Enumerate MOVDIRI instruction Fenghua Yu
2018-06-19  8:57   ` Thomas Gleixner
2018-06-19 21:36     ` Fenghua Yu
2018-06-19 22:32       ` Thomas Gleixner [this message]
2018-06-19 22:35         ` Fenghua Yu
2018-06-25 16:13       ` David Laight
2018-06-16  3:06 ` [RFC PATCH 2/8] x86/cpufeatures: Enumerate MOVDIR64B instruction Fenghua Yu
2018-06-16  3:06 ` [RFC PATCH 3/8] x86/cpufeatures: Enumerate UMONITOR, UMWAIT, and TPAUSE instructions Fenghua Yu
2018-06-16  3:06 ` [RFC PATCH 4/8] cpuidle: Set up maximum umwait time and umwait states Fenghua Yu
2018-06-19  9:03   ` Thomas Gleixner
2018-06-19 15:46     ` Fenghua Yu
2018-06-16  3:06 ` [RFC PATCH 5/8] x86/umwait.c: Add sysfs interface to show tsc_khz Fenghua Yu
2018-06-19  9:08   ` Thomas Gleixner
2018-06-19 15:11     ` Fenghua Yu
2018-06-16  3:06 ` [RFC PATCH 6/8] x86/lib_direct_store.h: Add APIs for direct store instructions Fenghua Yu
2018-06-19  8:47   ` Thomas Gleixner
2018-06-16  3:06 ` [RFC PATCH 7/8] x86/lib_user_wait.h: Add APIs for user wait instructions Fenghua Yu
2018-06-19  9:12   ` Thomas Gleixner
2018-06-19 22:27     ` Fenghua Yu
2018-06-19 22:34       ` Thomas Gleixner
2018-06-19 22:36         ` Fenghua Yu
2018-06-16  3:06 ` [RFC PATCH 8/8] selftests/x86: Self test for the APIs in lib_direct_store.h and lib_user_wait.h Fenghua Yu

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