Re: [Xen-devel] Re : Re : task btrfs-transacti:651 blocked for more than 120 seconds

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Sep 28, 2017 at 05:27:54PM +0000, Olivier Bonvalet wrote:
> Le jeudi 28 septembre 2017 à 17:12 +0100, Roger Pau Monné a écrit :
> > 
> > Quite likely. With so many PV block devices attached you either have
> > to limit the number of queues and persistent grants per-device, or
> > expand the number of grants allowed by Xen.
> > 
> > Can you try to set the following in the Xen command line [0] and see
> > if that solves your issues:
> > 
> > gnttab_max_frames=64
> > 
> > Roger.
> > 
> > [0] http://xenbits.xenproject.org/docs/unstable/misc/xen-command-line
> > .html
> > 
> > _______________________________________________
> > 
> 
> Oh, from the Novell's documentation [0] I read :
> 
> « General recommendation for determining the proper value for
> "gnttab_max_frames" is to multiply by 2 the number of attached disks. »
> 
> 
> Since I have about 250 RBD devices, I suppose I have to try directly
> with gnttab_max_frames=512, right ?

Do you have 250 devices attached to the same guest? If so I guess 512
might be sensible, although you said earlier that you had 26 devices
attached, not 250.

Roger.

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