Hi, I''m playing around with Xen 4 for the first time on a machine with a serial console and I''m seeing some odd behaviour with a slow (9600 baud) serial console and the hypervisor. Basically Xen is producing a vast amount of console output during boot, and at some point after the dom0 kernel has been loaded it will just stop printing it to the serial console. The point it does this at isn''t deterministic. Nothing more gets printed. It''s often part way through printing even the prefix, like: [ 0.0000 or similar. If I tap a key at this point then I get a login prompt from getty on hvc0 as I would expect. Everything appears to be working in fact; it''s almost like as soon as init in dom0 decided to put a getty on hvc0, Xen gives up on its backlog of things to print on console. I added the sync_console boot parameter, and with this everything is printed from start of boot to login prompt on hvc0. I also get this warning however: (XEN) ********************************************** (XEN) ******* WARNING: CONSOLE OUTPUT IS SYNCHRONOUS (XEN) ******* This option is intended to aid debugging of Xen by ensuring (XEN) ******* that all output is synchronously delivered on the serial line. (XEN) ******* However it can introduce SIGNIFICANT latencies and affect (XEN) ******* timekeeping. It is NOT recommended for production use! (XEN) ********************************************** which makes me think that maybe it isn''t a good idea to keep that set. There are none of these problems using the same kernel on bare metal. I''m unable to easily attach a VGA monitor so I''m not sure what it looks like on there. In terms of grub settings I am using those recommended in http://wiki.debian.org/Xen#Dom0_.28host.29 under "Serial console access", but I''ve tried what seems like every possible combination and nothing makes any difference to this phenomenon except sync_console. Any ideas? Cheers, Andy _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Hello, [ This is in reply to an unanswered post of mine at http://is.gd/KRrLGo ] On Sat, Apr 23, 2011 at 03:22:18AM +0000, Andy Smith wrote:> I''m seeing some odd behaviour with a slow (9600 baud) serial > console and the hypervisor. > > Basically Xen is producing a vast amount of console output during > boot, and at some point after the dom0 kernel has been loaded it > will just stop printing it to the serial console.I never got an answer to this on-list, so for the sake of the archives... Keir advised: If you want to capture all Xen''s boot output, the safest way is to increase the serial transmit buffer size. Try adding serial_tx_buffer=64k to the Xen command line. I have now had chance to test this, and it does indeed work perfectly for me; much better than using sync_console. Thanks! Andy _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users