linux-kernel - Re: [PATCH v2 7/7] driver-core: add preferred async probe option for built-in and modules

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Message-ID: <20141007173404.GB31328@mtj.dyndns.org>
Date:	Tue, 7 Oct 2014 13:34:04 -0400
From:	Tejun Heo <tj@...nel.org>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	gregkh@...uxfoundation.org, dmitry.torokhov@...il.com,
	tiwai@...e.de, arjan@...ux.intel.com, teg@...m.no,
	rmilasan@...e.com, werner@...e.com, oleg@...hat.com, hare@...e.com,
	bpoirier@...e.de, santosh@...lsio.com, pmladek@...e.cz,
	dbueso@...e.com, linux-kernel@...r.kernel.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Kay Sievers <kay@...y.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tim Gardner <tim.gardner@...onical.com>,
	Pierre Fersing <pierre-fersing@...rref.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	Casey Leedom <leedom@...lsio.com>,
	Hariprasad S <hariprasad@...lsio.com>,
	MPT-FusionLinux.pdl@...gotech.com, linux-scsi@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2 7/7] driver-core: add preferred async probe option for
 built-in and modules

Hello,

On Tue, Oct 07, 2014 at 01:10:46AM +0200, Luis R. Rodriguez wrote:
> On Mon, Oct 06, 2014 at 05:01:18PM -0400, Tejun Heo wrote:
> > For in-kernel stuff, we already have a clear
> > synchronization point where we already synchronize all async calls.
> > Shouldn't we be flushing these async probes there too?
> 
> This seems to be addressing if what I meant by prepared, "ready", so let
> me address this as I do think its important.
> 
> By async calls do you mean users of async_schedule()? I see it

Yes.

> also uses system_unbound_wq as well but I do not see anyone calling
> flush_workqueue(system_unbound_wq) on the kernel. We do use
> async_synchronize_full() on kernel_init() but that just waits.

But you can create a new workqueue and queue all the async probing
work items there and flush the workqueue right after
async_synchronize_full().

...
> bus.enable_kern_async=1 would still also serve as a helper for the driver core
> to figure out if it should use async probe then on modules if prefer_async_probe
> was enabled. Let me know if you figure out a way to avoid it.

Why do we need the choice at all?  It always should, no?

Thanks.

-- 
tejun
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