From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 729A16B0022 for ; Thu, 28 Apr 2011 11:12:10 -0400 (EDT) Received: by fxm18 with SMTP id 18so2763225fxm.14 for ; Thu, 28 Apr 2011 08:12:07 -0700 (PDT) Date: Thu, 28 Apr 2011 17:12:03 +0200 From: Tejun Heo Subject: Re: [PATCH] percpu: preemptless __per_cpu_counter_add Message-ID: <20110428151203.GE16552@htj.dyndns.org> References: <20110427102034.GE31015@htj.dyndns.org> <1303961284.3981.318.camel@sli10-conroe> <20110428100938.GA10721@htj.dyndns.org> <20110428142331.GA16552@htj.dyndns.org> <20110428144446.GC16552@htj.dyndns.org> <20110428145657.GD16552@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Shaohua Li , Eric Dumazet , "akpm@linux-foundation.org" , "linux-mm@kvack.org" On Thu, Apr 28, 2011 at 10:05:09AM -0500, Christoph Lameter wrote: > On Thu, 28 Apr 2011, Tejun Heo wrote: > > Gees, Christoph. That is a test case to show the issue prominently, > > which is what a test case is supposed to do. What it means is that > > _any_ update can trigger @batch deviation on _sum() regardless of its > > frequency or concurrency level and that's the nastiness I've been > > talking about over and over again. > > As far as I understand it: This is a test case where you want to show us > the atomic_t type behavior of _sum. This only works in such an artificial > test case. In reality batches of updates will modify any 'accurate' result > that you may have obtained from the _sum function. It seems like we can split hairs all day long about the similarities and differences with atomics, so let's forget about atomics for now. I don't like any update having possibility of causing @batch jumps in _sum() result. That severely limits the usefulness of hugely expensive _sum() and the ability to scale @batch. Not everything in the world is vmstat. Think about other _CURRENT_ use cases in filesystems. -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org