From: Paolo Bonzini <pbonzini@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: rkrcmar@redhat.com, David Hildenbrand <dahi@linux.vnet.ibm.com>,
David Matlack <dmatlack@google.com>,
Jens Freimann <jfrei@linux.vnet.ibm.com>
Subject: Re: [PATCH] KVM: add halt_attempted_poll to VCPU stats
Date: Wed, 16 Sep 2015 12:15:22 +0200 [thread overview]
Message-ID: <55F9413A.8000006@redhat.com> (raw)
In-Reply-To: <55F9409B.9020501@de.ibm.com>
On 16/09/2015 12:12, Christian Borntraeger wrote:
> I am looking into a case right now, where auto polling goes
> completely nuts on my system:
>
> guest1: 8vcpus guest2: 1 vcpu
> iperf with 25 process (-P25) from guest1 to guest2.
>
> I/O interrupts on s390 are floating (pending on all CPUs) so on
> ALL VCPUs that go to sleep, polling will consider any pending
> network interrupt as successful poll. So with auto polling the
> guest consumes up to 5 host CPUs without auto polling only 1.
> Reducing halt_poll_ns to 100000 seems to work (goes back to
> 1 cpu).
>
> The proper way might be to feedback the result of the
> interrupt dequeue into the heuristics. Don't know yet how
> to handle that properly.
I think it's simplest to disable halt_poll_ns by default on s390. On
x86, for example, you can mark interrupts so that they _can_ be
delivered to all CPUs but only one will get it.
You can add a Kconfig symbol for that to other architectures, and not s390.
Paolo
next prev parent reply other threads:[~2015-09-16 10:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1442334477-35377-1-git-send-email-pbonzini@redhat.com>
2015-09-15 17:21 ` [PATCH] KVM: add halt_attempted_poll to VCPU stats David Matlack
2015-09-16 10:12 ` Christian Borntraeger
2015-09-16 10:15 ` Paolo Bonzini [this message]
2015-09-16 12:12 ` Wanpeng Li
2015-09-17 10:28 ` David Hildenbrand
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