linux-kernel - Re: [Query] Preemption (hogging) of the work handler

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Message-ID: <CAJZ5v0ggjER5soi35bvNHTxGLYK7pie_DxtZKQHSvdH6wFf9AA@mail.gmail.com>
Date:	Thu, 14 Jul 2016 03:09:01 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>, Jan Kara <jack@...e.cz>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, Tejun Heo <tj@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	vlevenetz@...sol.com,
	Vaibhav Hiremath <vaibhav.hiremath@...aro.org>,
	Alex Elder <alex.elder@...aro.org>, johan@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Petr Mladek <pmladek@...e.com>
Subject: Re: [Query] Preemption (hogging) of the work handler

On Thu, Jul 14, 2016 at 2:55 AM, Sergey Senozhatsky
<sergey.senozhatsky.work@...il.com> wrote:
> Hello,
>
> On (07/13/16 08:39), Viresh Kumar wrote:
> [..]
>> Maybe not, as this can still lead to the original bug we were all
>> chasing. This may hog some other CPU if we are doing excessive
>> printing in suspend :(
>
> excessive printing is just part of the problem here. if we cab cond_resched()
> in console_unlock() (IOW, we execute console_unlock() with preemption and
> interrupts enabled) then everything must be ok, and *from printing POV* there
> is no difference whether it's printk_kthread or anything else in this case.
> the difference jumps in when original console_unlock() is executed with
> preemption/irq disabled, then offloading it to schedulable printk_kthread is
> the right thing.
>
>> suspend_console() is called quite early, so for example in my case we
>> do lots of printing during suspend (not from the suspend thread, but
>> an IRQ handled by the USB subsystem, which removes a bus with help of
>> some other thread probably).
>
> a silly question -- can we suspend consoles later?

Not really and I'm not sure how that would help?