From mboxrd@z Thu Jan  1 00:00:00 1970
From: Rik van Riel <riel@redhat.com>
Subject: Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq
Date: Wed, 14 Jan 2015 13:22:43 -0500
Message-ID: <54B6B3F3.2000908@redhat.com>
References: <20150114171251.882318257@redhat.com> <20150114171459.593877145@redhat.com>
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Cc: Luiz Capitulino <lcapitulino@redhat.com>,
	Steven Rostedt <srostedt@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>, kvm@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>,
	linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
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On 01/14/2015 12:12 PM, Marcelo Tosatti wrote:
> The problem:
> 
> On -RT, an emulated LAPIC timer instances has the following path:
> 
> 1) hard interrupt
> 2) ksoftirqd is scheduled
> 3) ksoftirqd wakes up vcpu thread
> 4) vcpu thread is scheduled
> 
> This extra context switch introduces unnecessary latency in the 
> LAPIC path for a KVM guest.

> This patch reduces the average latency in my tests from 14us to 11us.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Acked-by: Rik van Riel <riel@redhat.com>