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[Xen-devel] Relevance of global lock (/var/lock/xl) in xl tool


  • To: xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Michał Leszczyński <michal.leszczynski@xxxxxxx>
  • Date: Fri, 7 Jun 2019 14:06:30 +0200 (CEST)
  • Delivery-date: Fri, 07 Jun 2019 13:13:18 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Thread-index: pEodq5Ko/lTM9QxESyajbye9qRVVNw==
  • Thread-topic: Relevance of global lock (/var/lock/xl) in xl tool

Hello,

when either "xl restore" or "xl create" command is invoked, a global lock is 
acquired here:

https://github.com/xen-project/xen/blob/master/tools/xl/xl_vmcontrol.c#L876

I'm trying to figure out what is the exact importance of this lock? Is it 
really critical for XL operation? I have a pretty powerful machine on which I 
want to run a few dozen of short-lived VMs. This lock is seriously slowing me 
down, not letting to restore more than one domain at once. Turns out that 
everything still works fine (and much faster) when I comment-out the lock in 
the abovementioned place, but I'm not sure if it's a correct impression.

Does anyone know if there is a situation in which Xen would screw up without 
this lock?


Best regards,
Michał Leszczyński

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