Re: [PATCH RFC V4 0/5] kvm : Paravirt-spinlock support for KVM guests

From: Alexander Graf <agraf@suse.de>
To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
	Greg Kroah-Hartman <gregkh@suse.de>,
	linux-doc@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
	Paul Mackerras <paulus@samba.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Xen <xen-devel@lists.xensource.com>,
	Dave Jiang <dave.jiang@intel.com>, KVM <kvm@vger.kernel.org>,
	Glauber Costa <glommer@redhat.com>, X86 <x86@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Avi Kivity <avi@redhat.com>,
	Rik van Riel <riel@redhat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Sasha Levin <levinsasha928@gmail.com>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Virtualization <virtualization@lists.linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Dave Hansen <dave@linu
Subject: Re: [PATCH RFC V4 0/5] kvm : Paravirt-spinlock support for KVM guests
Date: Mon, 16 Jan 2012 19:42:38 +0100	[thread overview]
Message-ID: <E9F33AFD-F051-4D68-84FF-D259FD6AD19D@suse.de> (raw)
In-Reply-To: <4F146EA5.3010106@linux.vnet.ibm.com>

On 16.01.2012, at 19:38, Raghavendra K T wrote:

> On 01/16/2012 07:53 PM, Alexander Graf wrote:
>> 
>> On 16.01.2012, at 15:20, Srivatsa Vaddagiri wrote:
>> 
>>> * Alexander Graf<agraf@suse.de>  [2012-01-16 04:57:45]:
>>> 
>>>> Speaking of which - have you benchmarked performance degradation of pv ticket locks on bare metal?
>>> 
>>> You mean, run kernel on bare metal with CONFIG_PARAVIRT_SPINLOCKS
>>> enabled and compare how it performs with CONFIG_PARAVIRT_SPINLOCKS disabled for
>>> some workload(s)?
>> 
>> Yup
>> 
>>> 
>>> In some sense, the 1x overcommitcase results posted does measure the overhead
>>> of (pv-)spinlocks no? We don't see any overhead in that case for atleast
>>> kernbench ..
>>> 
>>>> Result for Non PLE machine :
>>>> ============================
>>> 
>>> [snip]
>>> 
>>>> Kernbench:
>>>>               BASE                    BASE+patch
>> 
>> What is BASE really? Is BASE already with the PV spinlocks enabled? I'm having a hard time understanding which tree you're working against, since the prerequisites aren't upstream yet.
>> 
>> 
>> Alex
> 
> Sorry for confusion, I think I was little imprecise on the BASE.
> 
> The BASE is pre 3.2.0 + Jeremy's following patches:
> xadd (https://lkml.org/lkml/2011/10/4/328)
> x86/ticketlocklock  (https://lkml.org/lkml/2011/10/12/496).
> So this would have ticketlock cleanups from Jeremy and
> CONFIG_PARAVIRT_SPINLOCKS=y
> 
> BASE+patch = pre 3.2.0 + Jeremy's above patches + above V5 PV spinlock
> series and CONFIG_PARAVIRT_SPINLOCKS=y
> 
> In both the cases  CONFIG_PARAVIRT_SPINLOCKS=y.
> 
> So let,
> A. pre-3.2.0 with CONFIG_PARAVIRT_SPINLOCKS = n
> B. pre-3.2.0 + Jeremy's above patches with CONFIG_PARAVIRT_SPINLOCKS = n
> C. pre-3.2.0 + Jeremy's above patches with CONFIG_PARAVIRT_SPINLOCKS = y
> D. pre-3.2.0 + Jeremy's above patches + V5 patches with CONFIG_PARAVIRT_SPINLOCKS = n
> E. pre-3.2.0 + Jeremy's above patches + V5 patches with CONFIG_PARAVIRT_SPINLOCKS = y
> 
> is it performance of A vs E ? (currently C vs E)

Since D and E only matter with KVM in use, yes, I'm mostly interested in A, B and C :).

Alex