From mboxrd@z Thu Jan  1 00:00:00 1970
From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Subject: Re: [PATCH RFC V4 0/5] kvm : Paravirt-spinlock support for KVM guests
Date: Wed, 25 Jan 2012 23:15:36 +0530
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To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.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>, 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>, Stefano Stabellini <stefano.stabellini@eu.citrix.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@linux.vnet.ibm.com>, Suzuki Poulose <suzuki@linux.vn>
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On 01/25/2012 10:05 PM, Konrad Rzeszutek Wilk wrote:
>> So it seems we have worst case overhead of around 8%. But we see
>> improvement of at-least 15% once when little more time is spent in
>> critical section.
>
> Is this with collecting the histogram information about spinlocks? We found
> that if you enable that for production runs it makes them quite slower.
>

Ok. Are you referring to CONFIG_KVM_DEBUG_FS/CONFIG_XEN_DEBUG_FS?. Not
it was not enabled. But then may be I was not precise. This test was 
only on native. So it should have not affected IMO.

It is nice to know that histogram affects, since I was always under the
impression that it does not affect much on guest too. My experiments
had almost always enabled that.

Let me know if you referred to something else..