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From: David Miller <davem@davemloft.net>
To: borntraeger@de.ibm.com
Cc: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org,
	kvm@vger.kernel.org, peterz@infradead.org,
	heiko.carstens@de.ibm.com, linux-kernel@vger.kernel.org,
	npiggin@gmail.com, virtualization@lists.linux-foundation.org,
	noamc@ezchip.com, schwidefsky@de.ibm.com,
	xen-devel@lists.xenproject.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH/RFC 0/5] cpu_relax: introduce yield, remove lowlatency
Date: Fri, 21 Oct 2016 11:12:19 -0400 (EDT)	[thread overview]
Message-ID: <20161021.111219.988688105971081562.davem__33394.9184547693$1477062783$gmane$org@davemloft.net> (raw)
In-Reply-To: <2cf23cb7-05c5-0a2d-2ed5-aa90d582f802@de.ibm.com>

From: Christian Borntraeger <borntraeger@de.ibm.com>
Date: Fri, 21 Oct 2016 17:08:54 +0200

> On 10/21/2016 04:57 PM, David Miller wrote:
>> From: Christian Borntraeger <borntraeger@de.ibm.com>
>> Date: Fri, 21 Oct 2016 13:58:53 +0200
>> 
>>> For spinning loops people did often use barrier() or cpu_relax().
>>> For most architectures cpu_relax and barrier are the same, but on
>>> some architectures cpu_relax can add some latency. For example on s390
>>> cpu_relax gives up the time slice to the hypervisor. On power cpu_relax
>>> tries to give some of the CPU to the neighbor threads. To reduce the
>>> latency another variant cpu_relax_lowlatency was introduced. Before this
>>> is used in more and more places, lets revert the logic of provide a new
>>> function cpu_relax_yield that can spend some time and for s390 yields
>>> the guest CPU.
>> 
>> Sparc64, fwiw, behaves similarly to powerpc.
> 
> As sparc currently defines cpu_relax_lowlatency to cpu_relax, this patch set
> should be a no-op then for sparc, correct?
> 
> My intend was that cpu_relax should not add a huge latency but can certainly
> push some cpu power to hardware threads of the same core. This seems to be
> the case for sparc/power and some arc variants. 

Agreed.

  reply	other threads:[~2016-10-21 15:12 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-21 11:58 [PATCH/RFC 0/5] cpu_relax: introduce yield, remove lowlatency Christian Borntraeger
2016-10-21 11:58 ` [PATCH 1/5] processor.h: introduce cpu_relax_yield Christian Borntraeger
2016-10-21 11:58 ` [PATCH 2/5] stop_machine: yield CPU during stop machine Christian Borntraeger
2016-10-21 12:05   ` Peter Zijlstra
2016-10-21 12:05     ` Peter Zijlstra
2016-10-21 12:41     ` Juergen Gross
2016-10-21 12:41     ` Juergen Gross
2016-10-21 12:41     ` Juergen Gross
2016-10-22  0:06     ` Nicholas Piggin
2016-10-24  7:52       ` Christian Borntraeger
2016-10-24  7:52         ` Christian Borntraeger
2016-10-24  8:47         ` Peter Zijlstra
2016-10-24  8:47           ` Peter Zijlstra
2016-10-22  0:06     ` Nicholas Piggin
2016-10-21 11:58 ` [PATCH 3/5] s390: make cpu_relax a barrier again Christian Borntraeger
2016-10-21 11:58 ` [PATCH 4/5] Remove cpu_relax_lowlatency users Christian Borntraeger
2016-10-21 11:58 ` [PATCH 5/5] remove cpu_relax_lowlatency Christian Borntraeger
2016-10-21 12:06 ` [PATCH/RFC 0/5] cpu_relax: introduce yield, remove lowlatency Peter Zijlstra
2016-10-21 14:57 ` David Miller
2016-10-21 15:08   ` Christian Borntraeger
2016-10-21 15:08     ` Christian Borntraeger
2016-10-21 15:12     ` David Miller [this message]
2016-10-21 15:12     ` David Miller
2016-10-21 15:12     ` David Miller
2016-10-21 15:08   ` Christian Borntraeger

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