From: Oliver Neukum <oliver@neukum.org>
To: linux-usb-devel@lists.sourceforge.net
Subject: Re: [linux-usb-devel] Re: [PATCH 00/10] usb-serial: Switches from spin lock to atomic_t.
Date: Tue, 6 Dec 2005 23:48:14 +0100
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Cc: Eduardo Pereira Habkost <ehabkost@mandriva.com>, Greg KH <gregkh@suse.de>,
       Luiz Fernando Capitulino <lcapitulino@mandriva.com.br>,
       linux-kernel@vger.kernel.org
References: <20051206095610.29def5e7.lcapitulino@mandriva.com.br> <20051206194041.GA22890@suse.de> <20051206201340.GB20451@duckman.conectiva>
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Am Dienstag, 6. Dezember 2005 21:13 schrieb Eduardo Pereira Habkost:
> Anyway, I don't see yet why the atomic_t would make the code slower on
> non-smp. Is atomic_add_unless(v, 1, 1) supposed to be slower than
> 'if (!v) v = 1;' ?

spin_lock() can be dropped on UP. atomic_XXX must either use an operation
on main memory, meaning less efficient code generation, or must disable
interrupts even on UP.

	Regards
		Oliver
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