Messages in this thread |  | | From | (Eric W. Biederman) | Date | Sun, 09 Apr 2017 13:21:44 -0500 | Subject | Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test_stage |
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Sergey Senozhatsky <sergey.senozhatsky@gmail.com> writes:
> On (04/07/17 17:23), Peter Zijlstra wrote: > [..] >> > we are looking at different typical setups :) serial console being 45 >> > seconds behind logbuf does not surprise me anymore. >> >> That does sound like you're doing something wrong and should look at >> reducing printk() more than anything else. > > yeah, 45sec is an extreme case that simply doesn't surprise me anymore ;) > that's not a normal/usual delay, of course, we are not this mad. on average > it's much better and may be not so far 2 seconds after all. a massive OOM > report, of course, appends logbuf messages at a much higher rate than UART > serial console can swallow, so the delay is getting larger, expectedly. > and, no, I don't add any printk-s, I'm looking at the lockup reports
Are you running your serial consoles at 9600 baud?
I would think the first thing to do would be to up your serial console baud rate to 115200 or at least 38400.
Similarly anything the kernel is certain to survive I would set loglevel such that it is logging somewhere with syslog rather than printk.
Of course my expectation on a production machine is to have panic on oom set, to print the huge OOM message and then reboot. So I don't possibly see how offloading to another thread and then switching right back to emergency mode is at all practical to solve the delay for a serious situation like OOM.
It sounds like you are blaming printk when the problem is a very slow logging device.
Eric
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