Messages in this thread | | | Date | Mon, 12 Oct 2009 15:25:03 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] panic.c: export panic_on_oops |
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* Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> > See my reply to David Woodhouse, i think we should add support for > > buffering in kernel/printk.c and that would both fix your problems, > > would simplify the driver (significantly!) and would expose the > > generic buffering capability to other console drivers as well. > > Buffering printk in general is bad. [...]
The general (and default) case would be 0 buffering - i.e. finegrained per line calls to ->console_write().
This is the common case indeed, we want to get console output out as soon as possible and as finegrained as possible - as we dont know when a failure mode removes our ability to print anything else.
My argument is that instead of a complicated dance of workqueue versus non-workqueue printk support in the MTD code in drivers/mtd/mtdoops.c, this should be done at the generic console level.
It's not hard, nor complex if done at the right level, nor does it impact the regular zero-buffering codepath in a significant way - and the end result would be a significantly simpler (and, in turn, more robust) MTD printk driver.
I care about this because i still havent given up hope that the company you are working for will finally give us some permanent storage in the CPU itself, so that we can have cross-reboot printk buffering ;-) If that storage is in the form of Flash, then buffering (to optimize write cycles) is probably a must.
> [...] Given a driver needs only to provide about 6 lines of code using > a kfifo is it really that hard for the odd code that wants to buffer > to do that ?
Avoiding a workqueue in printk is about the critical path of failure and about complexity in general.
I dont see how kfifo helps here much - kfifo is really just a relatively simple dynamic memory buffer abstraction - while most of the complexity here is elsewhere. Could you explain what you meant with kfifo here please?
Ingo
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