From: Peter Zijlstra <peterz@infradead.org>
To: Oscar Salvador <osalvador@suse.de>
Cc: Juergen Gross <jgross@suse.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Ingo Molnar <mingo@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
linux-doc@vger.kernel.org, Waiman Long <longman@redhat.com>
Subject: Re: [PATCH resend] x86,kvm: Add a kernel parameter to disable PV spinlock
Date: Tue, 5 Sep 2017 10:07:26 +0200 [thread overview]
Message-ID: <20170905080726.7qp752syjo7u5nmz@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <bfb70a6a-a280-99a5-3282-af00cf6483ed@suse.de>
On Tue, Sep 05, 2017 at 08:57:16AM +0200, Oscar Salvador wrote:
> It may be that the original patch was just to keep consistency between Xen
> and KVM, and also only for testing purposes.
> But we find a case when a customer of ours is running some workloads with
> 1<->1 mapping between physical cores and virtual cores, and we realized that
> with the pv spinlocks disabled there is a 4-5% of performance gain.
There are very definite downsides to using a test-and-set spinlock.
A much better option would be one that forces the use of native
qspinlock in the 1:1 case. That means you have to fail both pv_enabled()
and virt_spin_lock().
next prev parent reply other threads:[~2017-09-05 8:07 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-04 14:28 [PATCH resend] x86,kvm: Add a kernel parameter to disable PV spinlock Oscar Salvador
2017-09-04 14:40 ` Peter Zijlstra
2017-09-04 19:32 ` Waiman Long
2017-09-04 22:21 ` Davidlohr Bueso
2017-09-05 6:28 ` Juergen Gross
2017-09-05 6:57 ` Oscar Salvador
2017-09-05 8:07 ` Peter Zijlstra [this message]
2017-09-05 6:58 ` Peter Zijlstra
2017-09-05 7:35 ` Juergen Gross
2017-09-05 8:10 ` Peter Zijlstra
2017-09-05 8:14 ` Juergen Gross
2017-09-05 8:28 ` Peter Zijlstra
2017-09-05 8:52 ` Juergen Gross
2017-09-05 9:03 ` Peter Zijlstra
2017-09-05 9:11 ` Juergen Gross
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