linux-kernel - Re: [PATCH] KVM: Remove deprecated create_singlethread

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Message-ID: <20160831142456.GL12660@htj.duckdns.org>
Date:   Wed, 31 Aug 2016 10:24:56 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Bhaktipriya Shridhar <bhaktipriya96@...il.com>
Cc:     Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] KVM: Remove deprecated create_singlethread_workqueue

On Tue, Aug 30, 2016 at 11:29:51PM +0530, Bhaktipriya Shridhar wrote:
> The workqueue "irqfd_cleanup_wq" queues a single work item
> &irqfd->shutdown and hence doesn't require ordering. It is a host-wide
> workqueue for issuing deferred shutdown requests aggregated from all
> vm* instances. It is not being used on a memory reclaim path.
> Hence, it has been converted to use system_wq.
> The work item has been flushed in kvm_irqfd_release().
> 
> The workqueue "wqueue" queues a single work item &timer->expired
> and hence doesn't require ordering. Also, it is not being used on
> a memory reclaim path. Hence, it has been converted to use system_wq.
> 
> System workqueues have been able to handle high level of concurrency
> for a long time now and hence it's not required to have a singlethreaded
> workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue
> created with create_singlethread_workqueue(), system_wq allows multiple
> work items to overlap executions even on the same CPU; however, a
> per-cpu workqueue doesn't have any CPU locality or global ordering
> guarantee unless the target CPU is explicitly specified and thus the
> increase of local concurrency shouldn't make any difference.
> 
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@...il.com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun