Re: xl dmesg buffer too small for Xen 4.18?

[Julien Grall <julien@xxxxxxx>]

(+Roger and moving to xen-devel)

Hi,

On 18/09/2023 19:17, Chuck Zmudzinski wrote:
> On 9/18/2023 9:00 AM, Chuck Zmudzinski wrote:
> > Hello,
> >
> > I tested Xen 4.18~rc0 on Alma Linux 9 and my first tests indicate it works fine 
> > for starting the guests I manage but I notice that immediately after boot and 
> > with only dom0 running on the system, I get:
> >
> > [user@Malmalinux ~]$ sudo xl dmesg
> > 00bee72000-00000bee72fff type=7 attr=000000000000000f
> > (XEN)  00000bee73000-00000bef49fff type=4 attr=000000000000000f
> > (XEN)  00000bef4a000-00000bef4bfff type=7 attr=000000000000000f
> > (XEN)  00000bef4c000-00000befbafff type=4 attr=000000000000000f
> > (XEN)  00000befbb000-00000befbbfff type=7 attr=000000000000000f
> > ...
> >
> > I have noticed the buffer fills up quickly on earlier Xen versions, but never 
> > have I seen it fill up during boot and with only dom0 running.
> >
> > Can increasing the buffer fix this? How would one do that?
> >
> > Thanks
> I see the setting is the command line option conring_size:
>
> https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html#conring_size
>
> The default is 16k, I tried 48k and that was big enough to capture all the 
> messages at boot for 4.18 rc0. This is probably not an issue if the release 
> candidate is being more verbose than the actual release will be. But if the 
> release is still this verbose, maybe the default of 16k should be increased.
Thanks for the report. This remind me the series [1] from Roger which 
tries to increase the default size to 32K. @Roger, I am wondering if we 
should revive it?
Cheers,

[1] 
https://lore.kernel.org/xen-devel/20220630082330.82706-1-roger.pau@xxxxxxxxxx/
--
Julien Grall