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Message-ID: <7cac7435-1f65-6a60-e2f5-ed5c285ea0ae@redhat.com>
Date: Thu, 26 May 2016 12:30:20 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org
Cc: Wanpeng Li <wanpeng.li@...mail.com>,
Radim Krčmář <rkrcmar@...hat.com>,
David Matlack <dmatlack@...gle.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Yang Zhang <yang.zhang.wz@...il.com>
Subject: Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers
On 26/05/2016 12:26, Paolo Bonzini wrote:
> As discussed on IRC, I would like to understand why the adaptive
> adjustment of halt_poll_ns is failing. It seems like you have so few
> halts that you don't get halt_poll_ns>0. Yet, when the VM halts, it's
> very close to the timer tick---often enough for this patch to have an
> effect.
>
> Please send a trace of halt_poll_ns_grow and halt_poll_ns_shrink
> tracepoints, so that we can find out more about this.
And 30 seconds after I wrote this email, you told me on IRC that the
guest had HZ=1000 and the module parameter was set to 1 ms in order to
_really_ benefit from the patch. So basically you could obtain the same
effect with idle=poll in the guest.
This explains why your reported results were not so great (as David noted).
Thanks,
Paolo
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