linux-kernel - Re: [PATCH v5 4/8] thunderbolt: Communication with the ICM (firmware)

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Message-ID: <20160729214838.GA14827@kroah.com>
Date:	Fri, 29 Jul 2016 14:48:38 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	Amir Levy <amir.jer.levy@...el.com>, andreas.noever@...il.com,
	bhelgaas@...gle.com, corbet@....net, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, netdev@...r.kernel.org,
	linux-doc@...r.kernel.org, thunderbolt-linux@...el.com,
	mika.westerberg@...el.com, tomas.winkler@...el.com
Subject: Re: [PATCH v5 4/8] thunderbolt: Communication with the ICM (firmware)

On Fri, Jul 29, 2016 at 02:02:24PM -0700, Stephen Hemminger wrote:
> On Thu, 28 Jul 2016 11:15:17 +0300
> Amir Levy <amir.jer.levy@...el.com> wrote:
> 
> > +static LIST_HEAD(controllers_list);
> > +static DECLARE_RWSEM(controllers_list_rwsem);
> 
> Why use a semaphore when simple spinlock or mutex would be better?

And never use a RW semaphore unless you can benchmark the difference
from a normal lock.  If you can't benchmark it, then don't use it...