Re: [Xen-devel] Help：Can xen restore several snapshots more faster at same time？

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Nov 06, 2017 at 04:38:51AM +0000, HUANG SHENGQIANG wrote:
> Dear XEN expert,
> 
> I find a blocker issue in my project. Would you please offer us some feedback?
> 
> The description from my development team:
> we need restore as much as xen snapshot at same times, but we found ‘xl 
> restore’ command is work linearly,  if we want to restore a new xen snapshot, 
> we need to wait for the previous snapshot finish it’s work. We try to debug 
> the xl source ,we found the follow information:
> [cid:image001.png@01D356F6.B8EE87E0]
> 

Please don't send pictures.

> When an snapshot is being restore, we can see another process is blocked.  We 
> trying to delete the acquire_lock from the source code , then we see all the 
> snapshots are being restore at same time, but restore is still very slow, one 
> snapshot needs about 25 seconds  to finish restore(our environment is cpu 
> E52620,  256G memory, SSD hard disk. The snapshot is Win7 OS with 2G memory).
> 

There is a lock in xl as you can see in the stack trace.

> So , does xen have the way to restore more faster when several snapshot is 
> restore at same time? Why KVM can restore several snapshot fast at same time? 
> (We try the same experiment in KVM, we got we can restore about 50+ snapshot 
> in 20S. )
> 

Part of the toolstack needs to be reworked. You can start by removing
the lock in xl to see what breaks.

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