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Re: [Qemu-devel] Lock contention in QEMU
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From: |
Paolo Bonzini |
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Subject: |
Re: [Qemu-devel] Lock contention in QEMU |
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Date: |
Thu, 15 Dec 2016 13:13:37 +0100 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 |
On 15/12/2016 09:04, Stefan Hajnoczi wrote:
>> Does this feature only work for VirtIO? Does it work for SCSI or IDE?
> This only works for virtio-blk and virtio-scsi. The virtio-scsi
> dataplane support is more recent and I don't remember if it is complete.
> I've CCed Fam and Paolo who worked on virtio-scsi dataplane.
>
> Now that you have mentioned that you aren't using virtio devices, there
> is another source of lock contention that you will encounter. I/O
> request submission takes place in the vcpu thread when ioeventfd is not
> used. Only virtio uses ioeventfd so your current QEMU configuration is
> unable to let the vcpu continue execution during I/O request submission.
>
> If you care about performance then using virtio devices is probably the
> best choice. Try comparing against virtio-scsi dataplane - you should
> see a lot less jitter.
Yes, virtio-scsi dataplane is complete.
Paolo
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