linux-kernel - Re: [PATCH 6/8] amd64_edac: enforce synchronous probe

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Message-ID: <20150318182318.GF11485@dtor-ws>
Date:	Wed, 18 Mar 2015 11:23:18 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Luis R . Rodriguez" <mcgrof@...e.com>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Olof Johansson <olof@...om.net>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH 6/8] amd64_edac: enforce synchronous probe

On Wed, Mar 18, 2015 at 02:16:52PM -0400, Tejun Heo wrote:
> Hello,
> 
> On Wed, Mar 18, 2015 at 10:45:44AM -0700, Dmitry Torokhov wrote:
> > Without the debug options how can we do that? I will definitely not be
> > able to go through all the in-tree drivers myself and see if they can be
> > asynchronously probed or not. The most I can do is to try enabling the
> > option on our side and fixing the drivers/subsystems that fail with
> > asynchronous probing. This will be iterative process for some time and
> > then we'll drop the debug option and flip the flag to do asynchronous
> > probing by default.
> 
> Is this even useful for most drivers?

Define useful. In my tests I was able to shave 2-3 seconds (out of 8-10)
of boot time for the board I was trying it on. Useful for our use case,
not so useful for others.

>  If not, let's just stick with
> whitelisting.  If it is useful, I worry that we're quite unlikely to
> build working blacklist with this approach.  idk, having both white
> and blacklists tend to end badly.

I will try fixing the amd64_edac driver, but I consider
FORCE_SYNCHRONOUS at the moment as an aid for use when trying
fully-asynchronous probing. OTOH I wonder how many more drivers do what
edac does and try to do post-binding setups... and whether it makes
sense to actually try and fix them.

Thanks.

-- 
Dmitry
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