Date: Tue, 6 Dec 2005 18:14:49 -0200
From: Luiz Fernando Capitulino <lcapitulino@mandriva.com.br>
To: Greg KH <gregkh@suse.de>
Cc: linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net,
       ehabkost@mandriva.com
Subject: Re: [PATCH 00/10] usb-serial: Switches from spin lock to atomic_t.
Message-Id: <20051206181449.11947f4f.lcapitulino@mandriva.com.br>
In-Reply-To: <20051206194041.GA22890@suse.de>
References: <20051206095610.29def5e7.lcapitulino@mandriva.com.br>
	<20051206194041.GA22890@suse.de>
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On Tue, 6 Dec 2005 11:40:41 -0800
Greg KH <gregkh@suse.de> wrote:

| On Tue, Dec 06, 2005 at 09:56:10AM -0200, Luiz Fernando Capitulino wrote:
| >  Greg,
| > 
| >  Don't get scared. :-)
| > 
| >  As showed by Eduardo Habkost some days ago, the spin lock 'lock' in the
| > struct 'usb_serial_port' is being used by some USB serial drivers to protect
| > the access to the 'write_urb_busy' member of the same struct.
| > 
| >  The spin lock however, is needless: we can change 'write_urb_busy' type
| > to be atomic_t and remove all the spin lock usage.
| 
| But if you do that, you make things slower on non-smp machines, which
| isn't very nice.  Why does the spinlock bother you?

 The spinlock makes the code less clear, error prone, and we already a
semaphore in the struct usb_serial_port.

 The spinlocks _seems_ useless to me.

-- 
Luiz Fernando N. Capitulino
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