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: <20141007175503.GE31328@mtj.dyndns.org>
Date:	Tue, 7 Oct 2014 13:55:03 -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 07:50:10PM +0200, Luis R. Rodriguez wrote:
> On Tue, Oct 07, 2014 at 01:34:04PM -0400, Tejun Heo wrote:
> > 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().
> 
> On second thought I would prefer to avoid this, I see this being good
> to help with old userspace but other than that I don't see a requirement
> for new userspace. Do you?

Hmmm... we batch up and do everything parallel, so I'm not sure how
much gain we'd be looking at by not waiting for at the end before
jumping into the userland.  Also, it's a bit of an orthogonal issue.
If we wanna skip such synchornization point before passing control to
userland, why are we applying that to this but not
async_synchronize_full() which has a far larger impact?  It's weird to
synchronize one while not the other, so yeah, if there are actual
benefits we can consider it but let's do it separately.

Thanks.

-- 
tejun
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