From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Zippel Date: Fri, 14 Jan 2005 03:39:16 +0000 Subject: Re: page table lock patch V15 [0/7]: overview Message-Id: <41E73EE4.50200@linux-m68k.org> List-Id: References: <41E4BCBE.2010001@yahoo.com.au> <20050112014235.7095dcf4.akpm@osdl.org> <20050112104326.69b99298.akpm@osdl.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Christoph Lameter Cc: Andrew Morton , nickpiggin@yahoo.com.au, torvalds@osdl.org, ak@muc.de, hugh@veritas.com, linux-mm@kvack.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org Hi, Christoph Lameter wrote: > Introduction of the cmpxchg is one atomic operations that replaces the two > spinlock ops typically necessary in an unpatched kernel. Obtaining the > spinlock requires an spinlock (which is an atomic operation) and then the > release involves a barrier. So there is a net win for all SMP cases as far > as I can see. But there might be a loss in the UP case. Spinlocks are optimized away, but your cmpxchg emulation enables/disables interrupts with every access. bye, Roman