Re: [PATCH] sched/fair: Use printk_deferred instead of printk in pick_eevdf()

[Chen Yu]

On 2023-10-10 at 16:12:44 +0200, Peter Zijlstra wrote:
> On Tue, Oct 10, 2023 at 08:26:00AM -0400, Phil Auld wrote:
> 
> > > No.. I detest printk_deferred with a passion. This is effectively a WARN
> > > and we don't do silly buggers for them either.
> > >
> > 
> > Sure, printk_deferred is not ideal, but is getting this message in the right
> > order worth locking up people's machines?  Not sure you get the message at
> > all when that happens.  I have to dig the code location out of the crash
> > dump to find which sched warning fired and took down the (usually virtual)
> > machine.
> 
> Same thing with WARN(), we don't have a silly bugger version of that
> either. Just use a sane printk() / console or whatever.
> 
> Virt stuff has perfectly functional serial consoles that works just fine
> and don't lock up the machine -- mostly. Use my early_printk hacks if
> you want something reliable:
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=debug/experimental
> 
> Boot with: "earlyprintk=serial,ttyS0,115200 force_early_printk". And all
> will be well.
> 
> The fact that crashdump is more reliable than printk is a *BIG* problem
> and the only solution is fixing printk() (people are sorta working on
> that). We should not try and work around this problem.
> 
> I fundamentally despise the delayed stuff, I've had countless insteances
> where delaying output means you have no output because the machine is
> dead.

I see, thanks for this information.

thanks,
Chenyu