From: Peter Zijlstra <peterz@infradead.org>
To: Rik van Riel <riel@redhat.com>
Cc: Waiman Long <Waiman.Long@hp.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
linux-arch@vger.kernel.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
xen-devel@lists.xenproject.org, kvm@vger.kernel.org,
Paolo Bonzini <paolo.bonzini@gmail.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
David Vrabel <david.vrabel@citrix.com>,
Oleg Nesterov <oleg@redhat.com>,
Daniel J Blueman <daniel@numascale.com>,
Scott J Norton <scott.norton@hp.com>,
Douglas Hatch <doug.hatch@hp.com>
Subject: Re: [PATCH v15 16/16] unfair qspinlock: a queue based unfair lock
Date: Thu, 9 Apr 2015 16:13:48 +0200 [thread overview]
Message-ID: <20150409141348.GX5029@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <55267BA8.9060009@redhat.com>
On Thu, Apr 09, 2015 at 09:16:24AM -0400, Rik van Riel wrote:
> On 04/09/2015 03:01 AM, Peter Zijlstra wrote:
> > On Wed, Apr 08, 2015 at 02:32:19PM -0400, Waiman Long wrote:
> >> For a virtual guest with the qspinlock patch, a simple unfair byte lock
> >> will be used if PV spinlock is not configured in or the hypervisor
> >> isn't either KVM or Xen. The byte lock works fine with small guest
> >> of just a few vCPUs. On a much larger guest, however, byte lock can
> >> have serious performance problem.
> >
> > Who cares?
>
> There are some people out there running guests with dozens
> of vCPUs. If the code exists to make those setups run better,
> is there a good reason not to use it?
Well use paravirt, !paravirt stuff sucks performance wise anyhow.
The question really is: is the added complexity worth the maintenance
burden. And I'm just not convinced !paravirt virt is a performance
critical target.
> Having said that, only KVM and Xen seem to support very
> large guests, and PV spinlock is available there.
>
> I believe both VMware and Hyperv have a 32 VCPU limit, anyway.
Don't we have Hyperv paravirt drivers? They could add support for
paravirt spinlocks too.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Rik van Riel <riel@redhat.com>
Cc: Waiman Long <Waiman.Long@hp.com>,
linux-arch@vger.kernel.org,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
Oleg Nesterov <oleg@redhat.com>,
kvm@vger.kernel.org,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Daniel J Blueman <daniel@numascale.com>,
x86@kernel.org, Paolo Bonzini <paolo.bonzini@gmail.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Scott J Norton <scott.norton@hp.com>,
Ingo Molnar <mingo@redhat.com>,
David Vrabel <david.vrabel@citrix.com>,
"H. Peter Anvin" <hpa@zytor.com>,
xen-devel@lists.xenproject.org,
Thomas Gleixner <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Douglas Hatch <doug.hatch@hp.com>
Subject: Re: [PATCH v15 16/16] unfair qspinlock: a queue based unfair lock
Date: Thu, 9 Apr 2015 16:13:48 +0200 [thread overview]
Message-ID: <20150409141348.GX5029@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <55267BA8.9060009@redhat.com>
On Thu, Apr 09, 2015 at 09:16:24AM -0400, Rik van Riel wrote:
> On 04/09/2015 03:01 AM, Peter Zijlstra wrote:
> > On Wed, Apr 08, 2015 at 02:32:19PM -0400, Waiman Long wrote:
> >> For a virtual guest with the qspinlock patch, a simple unfair byte lock
> >> will be used if PV spinlock is not configured in or the hypervisor
> >> isn't either KVM or Xen. The byte lock works fine with small guest
> >> of just a few vCPUs. On a much larger guest, however, byte lock can
> >> have serious performance problem.
> >
> > Who cares?
>
> There are some people out there running guests with dozens
> of vCPUs. If the code exists to make those setups run better,
> is there a good reason not to use it?
Well use paravirt, !paravirt stuff sucks performance wise anyhow.
The question really is: is the added complexity worth the maintenance
burden. And I'm just not convinced !paravirt virt is a performance
critical target.
> Having said that, only KVM and Xen seem to support very
> large guests, and PV spinlock is available there.
>
> I believe both VMware and Hyperv have a 32 VCPU limit, anyway.
Don't we have Hyperv paravirt drivers? They could add support for
paravirt spinlocks too.
next prev parent reply other threads:[~2015-04-09 14:14 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-08 18:32 [PATCH v15 16/16] unfair qspinlock: a queue based unfair lock Waiman Long
2015-04-08 18:32 ` Waiman Long
2015-04-09 7:01 ` Peter Zijlstra
2015-04-09 13:16 ` Rik van Riel
2015-04-09 13:16 ` Rik van Riel
2015-04-09 13:16 ` Rik van Riel
2015-04-09 14:13 ` Peter Zijlstra
2015-04-09 14:13 ` Peter Zijlstra [this message]
2015-04-09 14:13 ` Peter Zijlstra
2015-04-09 14:30 ` Rik van Riel
2015-04-09 14:30 ` Rik van Riel
2015-04-09 14:30 ` Rik van Riel
2015-04-09 21:52 ` Waiman Long
2015-04-09 21:52 ` Waiman Long
2015-04-09 21:52 ` Waiman Long
2015-04-09 7:01 ` Peter Zijlstra
2015-04-09 7:01 ` Peter Zijlstra
-- strict thread matches above, loose matches on Subject: below --
2015-04-08 18:32 Waiman Long
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