From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933036Ab2IFS3K (ORCPT ); Thu, 6 Sep 2012 14:29:10 -0400 Received: from merlin.infradead.org ([205.233.59.134]:45486 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932373Ab2IFS3H convert rfc822-to-8bit (ORCPT ); Thu, 6 Sep 2012 14:29:07 -0400 Message-ID: <1346956101.18408.61.camel@twins> Subject: Re: [PATCH tip/core/rcu 13/23] rcu: Control grace-period duration from sysfs From: Peter Zijlstra To: paulmck@linux.vnet.ibm.com Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Date: Thu, 06 Sep 2012 20:28:21 +0200 In-Reply-To: <20120906175324.GN2448@linux.vnet.ibm.com> References: <20120830181811.GA29154@linux.vnet.ibm.com> <1346350718-30937-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346350718-30937-13-git-send-email-paulmck@linux.vnet.ibm.com> <1346940930.18408.14.camel@twins> <20120906175324.GN2448@linux.vnet.ibm.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2012-09-06 at 10:53 -0700, Paul E. McKenney wrote: > > - how do I know if my workload wants a longer or shorter forced qs > > period? > > Almost everyone can do just fine with the defaults. If you have more > than about 1,000 CPUs, you might need a longer period. Because the cost of starting a grace period is on the same order (or larger) in cost as this period? > Some embedded > systems might need a shorter period -- the only specific example I know > of is network diagnostic equipment running wireshark, which starts up > slowly due to grace-period length. But but but 3 jiffies.. however is that too long? > > Also, whatever made you want to provide this 'feature' in the first > > place? > > Complaints from the two groups called out above. Does this really warrant a boot time knob for which even you cannot quite explain what values to use when?