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

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Message-ID: <20150318184550.GC25365@htj.duckdns.org>
Date:	Wed, 18 Mar 2015 14:45:50 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
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 11:37:31AM -0700, Dmitry Torokhov wrote:
> I do not believe that we will be able to activate asynchronous probing
> by default in the next 2, 3, 4 merge windows: distributions will have to
> try and use it and see if they are ready for it. However there are

Async provides strict completion ordering which storage drivers
already make use of to preserve probe order.  Why isn't this
transitive through asynchronous ->probe calls?  Shouldn't it be?

> drivers (slow to probe, usually input) that we do know are OK to be
> probed asynchronously even today (because the rest of the infrastructure
> dealing with input has been converted to deal with hotplug and devices
> coming and going in random order at random points of time). Thus
> whitelist is useful for now to reduce boot times even if the rest of the
> system is probed synchronously because you are not quite ready for your
> root device to jump around.

Yeah, I can see the short term benefits but at the same time I don't
think this is a healthy long term strategy unless someone really tries
to make it happen that three four merge window is gonna stretch
forever.  If storage drivers are problematic, why not just blacklist
them?

Thanks.

-- 
tejun
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