From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrea Arcangeli Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges Date: Fri, 29 Feb 2008 22:23:27 +0100 Message-ID: <20080229212327.GC8091@v2.random> References: <20080228005249.GF8091@v2.random> <20080228011020.GG8091@v2.random> <20080229005530.GO8091@v2.random> <20080229131302.GT8091@v2.random> <20080229201744.GB8091@v2.random> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Nick Piggin , steiner@sgi.com, Peter Zijlstra , linux-mm@kvack.org, Kanoj Sarcar , Roland Dreier , Steve Wise , linux-kernel@vger.kernel.org, Avi Kivity , kvm-devel@lists.sourceforge.net, daniel.blueman@quadrics.com, Robin Holt , general@lists.openfabrics.org, akpm@linux-foundation.org To: Christoph Lameter Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces@lists.sourceforge.net Errors-To: kvm-devel-bounces@lists.sourceforge.net List-Id: kvm.vger.kernel.org On Fri, Feb 29, 2008 at 01:03:16PM -0800, Christoph Lameter wrote: > That means we need both the anon_vma locks and the i_mmap_lock to become > semaphores. I think semaphores are better than mutexes. Rik and Lee saw > some performance improvements because list can be traversed in parallel > when the anon_vma lock is switched to be a rw lock. The improvement was with a rw spinlock IIRC, so I don't see how it's related to this. Perhaps the rwlock spinlock can be changed to a rw semaphore without measurable overscheduling in the fast path. However theoretically speaking the rw_lock spinlock is more efficient than a rw semaphore in case of a little contention during the page fault fast path because the critical section is just a list_add so it'd be overkill to schedule while waiting. That's why currently it's a spinlock (or rw spinlock). > Sounds like we get to a conceptually clean version here? I don't have a strong opinion if it should become a semaphore unconditionally or only with a CONFIG_XPMEM=y. But keep in mind preempt-rt runs quite a bit slower, or we could rip spinlocks out of the kernel in the first place ;) ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/