From: Stefan Hajnoczi <stefanha@gmail.com>
To: kalyan tata <manjulakalyan.tech@gmail.com>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] Performance Profiling 2 VMs
Date: Wed, 2 Mar 2016 11:28:49 +0000 [thread overview]
Message-ID: <20160302112849.GD11268@stefanha-x1.localdomain> (raw)
In-Reply-To: <CA+RW8bQFRj6FjNr7WhFpkdFkyT5ATQHiukKEE0KqDD-gA2QhJw@mail.gmail.com>
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On Tue, Mar 01, 2016 at 04:06:16PM -0800, kalyan tata wrote:
> Hi All,
>
> I am new to qemu development.
> Sorry If this is not the correct forum for this question, it would be great
> if you could direct me to correct forum.
>
> I am seeing very low virtio network throughput on an older (2.6.18) linux
> guest vs another newer guest (3.10) both running on the same host. (same
> config 2 vcpus, no multi Q etc.) I see very high CPU usage on the 2.6.18
> guest at very low network throughput and want to profile to find
> bottleneck.
>
> I tried to use "perf kvm" but the analysis shows overhead as max .25 %
> where as top in VM shows 100% cpu. (I used following as a guide
> https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/Virtualization_Tuning_and_Optimization_Guide/index.html#sect-Virtualization_Tuning_Optimization_Guide-Monitoring_Tools-perf_kvm
> )
>
> 0.25% :5235 [uhci_hcd] [g] 0xffffffff80182236
> 0.24% :5235 [uhci_hcd] [g] 0xffffffff8018226a
> 0.23% :5235 [virtio_ring] [g] vring_new_virtqueue
> 0.20% :5236 [uhci_hcd] [g] 0xffffffff80182236
> 0.18% :5236 [uhci_hcd] [g] 0xffffffff8018226a
> 0.18% :5235 [uhci_hcd] [g] 0xffffffff8016f385
> 0.14% :5236 [uhci_hcd] [g] 0xffffffff802fbe0f
> 0.14% :5235 [uhci_hcd] [g] 0xffffffff8001161a
> 0.14% :5235 [virtio_ring] [g] virtqueue_is_broken
>
>
> My basic question is - Is there a way I can profile the older version of
> linux guest so i can see the bottleneck (where the guest is spending CPU
> cycles) My aim is to see if i can patch the older version in the critical
> path with improvements made in newer version
What is the output of "mpstat 5" in the guest and on the host? mpstat
is part of the "sysstat" package.
mpstat is similar to vmstat but also shows "guest time" and "steal
time". Both are relevant to virtualization and will help show which
component is using so much CPU time.
Stefan
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next prev parent reply other threads:[~2016-03-02 11:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-02 0:06 [Qemu-devel] Performance Profiling 2 VMs kalyan tata
2016-03-02 11:28 ` Stefan Hajnoczi [this message]
2016-03-03 5:32 ` kalyan tata
2016-03-09 16:15 ` Stefan Hajnoczi
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