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Hi yunhong,
I agree with you of the taking I/O bandwidth as a resource, but it may be not so easy to implement.
Your another thinking about the launch time may be not so terrible, only the first boot it will be affected.

2014-02-17



Wangpan



发件人：yunhong jiang <yunhong.jiang at linux.intel.com>
发送时间：2014-02-15 08:21
主题：Re: [openstack-dev] [nova] Should we limit the disk IO bandwidth in copy_image while creating new instance?
收件人："OpenStack Development Mailing List (not for usage questions)"<openstack-dev at lists.openstack.org>
抄送：

On Fri, 2014-02-14 at 10:22 +0100, Sylvain Bauza wrote: 
> Instead of limitating the consumed bandwidth by proposiong a 
> configuration flag (yet another one, and which default value to be 
> set ?), I would propose to only decrease the niceness of the process 
> itself, so that other processes would get first the I/O access. 
> That's not perfect I assume, but that's a quick workaround limitating 
> the frustration. 
>  
>  
> -Sylvain 
>  
Decrease goodness is good for a short term, Some small concerns are, 
will that cause long launch time if the host is I/O intensive? And if 
launch time is billed also, then not fair for the new instance also. 

I think the ideal world is I/O QoS like through cgroup, take I/O 
bandwidth as a resource, and take the copy_image as an consumption of 
the I/O bandwidth resource. 

Thanks 
--jyh 
>  
> 2014-02-14 4:52 GMT+01:00 Wangpan <hzwangpan at corp.netease.com>: 
>         Currently nova doesn't limit the disk IO bandwidth in 
>         copy_image() method while creating a new instance, so the 
>         other instances on this host may be affected by this high disk 
>         IO consuming operation, and some time-sensitive business(e.g 
>         RDS instance with heartbeat) may be switched between master 
>         and slave. 
>           
>         So can we use the `rsync --bwlimit=${bandwidth} src dst` 
>         command instead of `cp src dst` while copy_image in 
>         create_image() of libvirt driver, the remote image copy 
>         operation also can be limited by `rsync --bwlimit= 
>         ${bandwidth}` or `scp -l=${bandwidth}`, this parameter 
>         ${bandwidth} can be a new configuration in nova.conf which 
>         allow cloud admin to config it, it's default value is 0 which 
>         means no limitation, then the instances on this host will be 
>         not affected while a new instance with not cached image is 
>         creating. 
>           
>         the example codes: 
>         nova/virt/libvit/utils.py: 
>         diff --git a/nova/virt/libvirt/utils.py 
>         b/nova/virt/libvirt/utils.py 
>         index e926d3d..5d7c935 100644 
>         --- a/nova/virt/libvirt/utils.py 
>         +++ b/nova/virt/libvirt/utils.py 
>         @@ -473,7 +473,10 @@ def copy_image(src, dest, host=None): 
>                  # sparse files.  I.E. holes will not be written to 
>         DEST, 
>                  # rather recreated efficiently.  In addition, since 
>                  # coreutils 8.11, holes can be read efficiently too. 
>         -        execute('cp', src, dest) 
>         +        if CONF.mbps_in_copy_image > 0: 
>         +            execute('rsync', '--bwlimit=%s' % 
>         CONF.mbps_in_copy_image * 1024, src, dest) 
>         +        else: 
>         +            execute('cp', src, dest) 
>              else: 
>                  dest = "%s:%s" % (host, dest) 
>                  # Try rsync first as that can compress and create 
>         sparse dest files. 
>         @@ -484,11 +487,22 @@ def copy_image(src, dest, host=None): 
>                      # Do a relatively light weight test first, so 
>         that we 
>                      # can fall back to scp, without having run out of 
>         space 
>                      # on the destination for example. 
>         -            execute('rsync', '--sparse', '--compress', 
>         '--dry-run', src, dest) 
>         +            if CONF.mbps_in_copy_image > 0: 
>         +                execute('rsync', '--sparse', '--compress', 
>         '--dry-run', 
>         +                        '--bwlimit=%s' % 
>         CONF.mbps_in_copy_image * 1024, src, dest) 
>         +            else: 
>         +                execute('rsync', '--sparse', '--compress', 
>         '--dry-run', src, dest) 
>                  except processutils.ProcessExecutionError: 
>         -            execute('scp', src, dest) 
>         +            if CONF.mbps_in_copy_image > 0: 
>         +                execute('scp', '-l', '%s' % 
>         CONF.mbps_in_copy_image * 1024 * 8, src, dest) 
>         +            else: 
>         +                execute('scp', src, dest) 
>                  else: 
>         -            execute('rsync', '--sparse', '--compress', src, 
>         dest) 
>         +            if CONF.mbps_in_copy_image > 0: 
>         +                execute('rsync', '--sparse', '--compress', 
>         +                        '--bwlimit=%s' % 
>         CONF.mbps_in_copy_image * 1024, src, dest) 
>         +            else: 
>         +                execute('rsync', '--sparse', '--compress', 
>         src, dest) 
>           
>           
>         2014-02-14 
>          
>         ______________________________________________________________ 
>         Wangpan 
>          
>         _______________________________________________ 
>         OpenStack-dev mailing list 
>         OpenStack-dev at lists.openstack.org 
>         http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev 
>          
>  
>  
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