From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v9 05/19] qspinlock: Optimize for smaller NR_CPUS Date: Thu, 17 Apr 2014 17:33:06 -0400 Message-ID: <53504892.60404@hp.com> References: <1397747051-15401-1-git-send-email-Waiman.Long@hp.com> <1397747051-15401-6-git-send-email-Waiman.Long@hp.com> <20140417155115.GQ11096@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140417155115.GQ11096@twins.programming.kicks-ass.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Peter Zijlstra Cc: linux-arch@vger.kernel.org, Rik van Riel , Raghavendra K T , Gleb Natapov , kvm@vger.kernel.org, Konrad Rzeszutek Wilk , Scott J Norton , x86@kernel.org, Paolo Bonzini , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Ingo Molnar , Chegu Vinod , David Vrabel , "H. Peter Anvin" , xen-devel@lists.xenproject.org, Thomas Gleixner , "Paul E. McKenney" , Linus Torvalds , Oleg Nesterov List-Id: virtualization@lists.linuxfoundation.org On 04/17/2014 11:51 AM, Peter Zijlstra wrote: > On Thu, Apr 17, 2014 at 11:03:57AM -0400, Waiman Long wrote: >> @@ -48,6 +53,9 @@ >> * We can further change the first spinner to spin on a bit in the lock word >> * instead of its node; whereby avoiding the need to carry a node from lock to >> * unlock, and preserving API. >> + * >> + * N.B. The current implementation only supports architectures that allow >> + * atomic operations on smaller 8-bit and 16-bit data types. >> */ > Only for the _Q_PENDING_BITS == 8 case, the other case should still be > fine. Yes, but _Q_PENDING_BITS is controlled by NR_CPUS which, for almost all the distributions, is less than 16K which means _Q_PENDING_BITS will always be set to 8, especially for non-x86 architectures. -Longman