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Re: [Qemu-devel] [PATCH v3] migration/block:limit the time used for bloc

From: Daniel P. Berrange
Subject: Re: [Qemu-devel] [PATCH v3] migration/block:limit the time used for block migration
Date: Wed, 5 Apr 2017 10:34:41 +0100
User-agent: Mutt/1.7.1 (2016-10-04)

On Wed, Apr 05, 2017 at 05:27:58PM +0800, address@hidden wrote:
> From: Lidong Chen <address@hidden>
> when migration with high speed, mig_save_device_bulk invoke
> bdrv_is_allocated too frequently, and cause vnc reponse slowly.
> this patch limit the time used for bdrv_is_allocated.

Can you explain why calling bdrv_is_allocated is impacting VNC performance ?

Migration is running in a background thread, so shouldn't be impacting the
main thread which handles VNC, unless the block layer is perhaps acquiring
the global qemu lock ? I wouldn't expect such a lock to be held for just
the bdrv_is_allocated call though.

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