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Re: Performance issues with /gnu/store in virtual machines

From: Ludovic Courtès
Subject: Re: Performance issues with /gnu/store in virtual machines
Date: Tue, 22 Aug 2017 16:35:35 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux)

Christopher Baines <address@hidden> skribis:

> On Tue, 22 Aug 2017 12:11:43 +0200
> address@hidden (Ludovic Courtès) wrote:
>> Hi Chris,
>> Christopher Baines <address@hidden> skribis:
>> >   1.13    0.000019           0      3853           openat  
>> [...]
>> >  13.56    0.193014          50      3853           openat  
>> So openat(2) is 4 orders of magnitude slower in the VM, which is a
>> problem.
>> I guess a large part of that is due to the fact that VM created with
>> ‘guix system vm’ use unionfs as their root file system, which is a
>> FUSE thing (see the “volatile” options in (gnu system vm), (gnu system
>> linux-initrd), and (gnu build linux-boot).)  I’m not sure how we could
>> avoid it.
> I'm unsure if the unionfs will be involved though, as find is searching
> in the /gnu/store directory, which is shared with the host:
>   TAG_gnu_store on /gnu/store type 9p (ro,relatime,sync,dirsync,trans=virtio)
> This might be misunderstanding how mounts work, but this could be
> either layered on top, or below the unionfs, and I'm guessing its on
> top, which in my mind would mean that the unionfs isn't involved?

Oh you’re probably right.  It might be that 9p over virtio is this slow.
We should look at what others are doing, I guess it’s a fairly common
use case.


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