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Date:   Fri, 19 Jan 2018 16:42:23 +0800
From:   Dave Young <dyoung@redhat.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc:     Andi Kleen <ak@linux.intel.com>, pmladek@suse.com,
        sergey.senozhatsky@gmail.com, rostedt@goodmis.org,
        linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        kexec@lists.infradead.org
Subject: Re: [PATCH] print kdump kernel loaded status in stack dump
Message-ID: <20180119084223.GC3985@dhcp-128-65.nay.redhat.com>
References: <20180117045057.GA4994@dhcp-128-65.nay.redhat.com>
 <878tcvt592.fsf@linux.intel.com>
 <20180119054538.GA484@jagdpanzerIV>
 <20180119081628.GB3985@dhcp-128-65.nay.redhat.com>
 <20180119082835.GA477@jagdpanzerIV>
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On 01/19/18 at 05:28pm, Sergey Senozhatsky wrote:
> On (01/19/18 16:16), Dave Young wrote:
> > On 01/19/18 at 02:45pm, Sergey Senozhatsky wrote:
> > > On (01/18/18 10:02), Andi Kleen wrote:
> > > > Dave Young <dyoung@redhat.com> writes:
> > > > >  		printk("%sHardware name: %s\n",
> > > > >  		       log_lvl, dump_stack_arch_desc_str);
> > > > > +	if (kexec_crash_loaded())
> > > > > +		printk("%skdump kernel loaded\n", log_lvl);
> > > > 
> > > > Oops/warnings are getting longer and longer, often scrolling away
> > > > from the screen, and if the kernel crashes backscroll does not work
> > > > anymore, so precious information is lost.
> > > 
> > > true. I even ended up having a console_reflush_on_panic() function. it
> > > simply re-prints with a delay [so I can at least read the oops] logbuf
> > > entries every once in a while, staring with the first oops_in_progress
> > > record.
> > > 
> > 
> > If too many messages printed on screen, then the next flush will 
> > still scroll up. 
> 
> right. but it re-prints Oops with a new console_unlock_delay() delay
> which gives me enough time to either read it as many times as I want,
> or take a picture, etc. it's not as fast as the normal oops print out.
> 
> [I'm not entirely sure I see why do we have printk_delay() in
>    vprintk_emit()... I mean I probably can see some reasoning behind
>    it, but at the same it makes sense to slow down console_unlock()
>    as well]

Looks like I am the guy who added the code :)  Actually no special
reason, just did not thinking about the performance issue at all at that
time..

> 
> 	-ss