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Re: [Xen-devel] [PATCH 2/2] locking/mutex, rwsem: Reduce vcpu_is_preempted() calling frequency
- To: Waiman Long <longman@xxxxxxxxxx>
- From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- Date: Wed, 8 Feb 2017 20:05:33 +0100
- Cc: linux-arch@xxxxxxxxxxxxxxx, Juergen Gross <jgross@xxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, x86@xxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, Radim Krčmář <rkrcmar@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Alok Kataria <akataria@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
- Delivery-date: Wed, 08 Feb 2017 19:05:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Wed, Feb 08, 2017 at 01:00:25PM -0500, Waiman Long wrote:
> As the vcpu_is_preempted() call is pretty costly compared with other
> checks within mutex_spin_on_owner() and rwsem_spin_on_owner(), they
> are done at a reduce frequency of once every 256 iterations.
That's just disgusting.
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