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

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Message-ID: <E607265CB020454880711A6F96C05A03971086A9@hasmsx108.ger.corp.intel.com>
Date:	Sun, 31 Jul 2016 10:18:29 +0000
From:	"Levy, Amir (Jer)" <amir.jer.levy@...el.com>
To:	Greg KH <gregkh@...uxfoundation.org>,
	Stephen Hemminger <stephen@...workplumber.org>
CC:	"andreas.noever@...il.com" <andreas.noever@...il.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"corbet@....net" <corbet@....net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	thunderbolt-linux <thunderbolt-linux@...el.com>,
	"Westerberg, Mika" <mika.westerberg@...el.com>,
	"Winkler, Tomas" <tomas.winkler@...el.com>
Subject: RE: [PATCH v5 4/8] thunderbolt: Communication with the ICM
 (firmware)

On Sat, Jul 30 2016, 12:48 AM, Greg KH wrote:
> 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...

I used RW semaphore since most of the time the list will be accessed for read.
Since it is used in non-time sensitive flows, I'll change it to mutex.