Re: xl dmesg buffer too small for Xen 4.18?

[Chuck Zmudzinski <brchuckz@xxxxxxxxxxxx>]

On 9/18/2023 2:49 PM, Julien Grall wrote:
> (+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/
> 

I just tested with 24k, and that is also big enough. So 32k would also be good. 
But the default of 16k appears to be too small for Xen 4.18 rc0 on my machine.