Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935682Ab3FTDXb (ORCPT ); Wed, 19 Jun 2013 23:23:31 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:24702 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935522Ab3FTDXa (ORCPT ); Wed, 19 Jun 2013 23:23:30 -0400 X-Authority-Analysis: v=2.0 cv=Du3UCRD+ c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=wom5GMh1gUkA:10 a=49Xwnclk0kMA:10 a=5SG0PmZfjMsA:10 a=kj9zAlcOel0A:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=aGTHLlSVUUYA:10 a=VwQbUJbxAAAA:8 a=U0FBzmo6wkCSSZAaCg0A:9 a=CjuIK1q_8ugA:10 a=LI9Vle30uBYA:10 a=-tA_eoRxER7jEvAP:21 a=lE4qiLz5Zc-u4H7M:21 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 74.67.115.198 Date: Wed, 19 Jun 2013 23:23:28 -0400 From: Steven Rostedt To: Rusty Russell Cc: Tejun Heo , "Paul E. McKenney" , Kent Overstreet , linux-kernel@vger.kernel.org, Linus Torvalds , Andrew Morton Subject: Re: A question on RCU vs. preempt-RCU Message-ID: <20130620032328.GC28618@home.goodmis.org> References: <20130616023611.GA19863@htj.dyndns.org> <8761xer1s8.fsf@rustcorp.com.au> <20130617182023.GH32663@mtj.dyndns.org> <87obb4ngdy.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87obb4ngdy.fsf@rustcorp.com.au> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1057 Lines: 23 On Tue, Jun 18, 2013 at 02:51:13PM +0930, Rusty Russell wrote: > Tejun Heo writes: > > Buth yeah, interesting trick. We'll be doing IPIs, flushing TLB and > > taking faults until it hits zero. It'll all depend on the frequency > > of preemption but given that branches don't tend to be too expensive > > on modern processors, maybe it'd be a bit too hairy for possibly > > marginal gain? > > Yeah, I'm not convinced either, but I am hoping some enthusiast will run > with the idea in hope of Fame and Glory :) This actually looks like a trick I think would be fun to implement. But as it being beneficial... the preempt count is used quite often, the fact that this page will be constantly in the TLB would have a bigger impact on general performance than saving the lousy branch. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/