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Re: [libvirt] [PATCH] blkio: change the minimum weight from 100 to 10



On 08/18/2013 11:59 PM, Gao feng wrote:
> kernel had changed the minimum weight of device blkio from
> 100 to 10 in commit df457f845e5449be2e7d96668791f789b3770ac7.
> 
> 	commit df457f845e5449be2e7d96668791f789b3770ac7
> 	Author: Justin TerAvest <teravest google com>
> 	Date:   Tue Mar 8 19:45:00 2011 +0100
> 
>           blk-cgroup: Lower minimum weight from 100 to 10.
> 
>  	   We've found that we still get good, useful isolation at weights this
>   	  low. I'd like to adjust the minimum so that any other changes can take
>   	  these values into account.
> 
>  	  Signed-off-by: Justin TerAvest <teravest google com>
>   	  Acked-by: Vivek Goyal <vgoyal redhat com>
> 	  Signed-off-by: Jens Axboe <jaxboe fusionio com>
> 
> libvirt should comport with kernel.
> 
> Signed-off-by: Gao feng <gaofeng cn fujitsu com>
> ---
>  docs/formatdomain.html.in |  4 ++--
>  src/util/vircgroup.c      | 10 +++++-----
>  2 files changed, 7 insertions(+), 7 deletions(-)

What happens when running a newer libvirt with an older kernel?  Or in
other words, what error message do you get if you pass a limit lower
than the current kernel can support?  I want to make sure the message
looks sane to an end-user before accepting this patch.

>  
> -    if (weight && (weight > 1000 || weight < 100)) {
> +    if (weight && (weight > 1000 || weight < 10)) {
>          virReportError(VIR_ERR_INVALID_ARG,
> -                       _("weight '%u' must be in range (100, 1000)"),
> +                       _("weight '%u' must be in range (10, 1000)"),
>                         weight);
>          return -1;

In other words, I suspect this code needs to be beefed up to actually
probe whether the kernel accepted the change, rather than blindly doing
the filter ourselves and hoping that it was correct.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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