Message-ID: <54D3C296.7030207@redhat.com>
Date: Thu, 05 Feb 2015 20:20:54 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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To: Jan Kiszka <jan.kiszka@siemens.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
CC: riel@redhat.com, rkrcmar@redhat.com, mtosatti@redhat.com
Subject: Re: [PATCH RFC] kvm: x86: add halt_poll module parameter
References: <1423152325-5094-1-git-send-email-pbonzini@redhat.com> <54D3BC94.9010007@siemens.com>
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On 05/02/2015 19:55, Jan Kiszka wrote:
> > This patch introduces a new module parameter for the KVM module; when it
> > is present, KVM attempts a bit of polling on every HLT before scheduling
> > itself out via kvm_vcpu_block.
>
> Wouldn't it be better to tune this on a per-VM basis? Think of mixed
> workloads with some latency-sensitive and some standard VMs.

Yes, but:

1) this turned out to be very cheap, so a per-host tunable is not too bad;

2) it also affects only very few workloads (for example network
workloads can already do polling in the guest) so it only affects few
people;

3) long term anyway we want it to auto tune, which is better than tuning
it per-VM.

Paolo
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