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Date: Thu, 8 May 2014 18:32:31 +0530
From: Amit Shah <amit.shah@redhat.com>
Message-ID: <20140508130231.GA24978@grmbl.mre>
References: <53693FA4.3000306@windriver.com> <5369D504.2070101@redhat.com>
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Subject: Re: [Qemu-devel] virtio-serial-pci very expensive during live
	migration
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To: Chris Friesen <chris.friesen@windriver.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, armbru@redhat.com

On (Wed) 07 May 2014 [16:25:50], Chris Friesen wrote:
> On 05/07/2014 12:39 AM, Paolo Bonzini wrote:
> >Il 06/05/2014 22:01, Chris Friesen ha scritto:
> >>
> >>It seems like the main problem is that we loop over all the queues,
> >>calling virtio_pci_set_host_notifier_internal() on each of them.  That
> >>in turn calls memory_region_add_eventfd(), which calls
> >>memory_region_transaction_commit(), which scans over all the address
> >>spaces, which seems to take the vast majority of the time.
> >
> >Yes, you can wrap the entire loop with memory_region_transaction_begin
> >and memory_region_transaction_commit.  Can you try that?
> 
> I tried the patch below.  Unfortunately it seems to cause qemu to crash.

This doesn't remove the memory_region_transaction_begin() and
_commit() from memory_region_add_eventfd(), which will still be
called.

Also, if you're not using all 32 ports, you can restrict the max
number of ports for a device using the
virtio-serial-pci.max_ports=uint32 property:

-device virtio-serial-pci,max_ports=2

		Amit