From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f181.google.com (mail-pd0-f181.google.com [209.85.192.181]) by kanga.kvack.org (Postfix) with ESMTP id 293CB6B00AA for ; Tue, 6 Jan 2015 03:09:49 -0500 (EST) Received: by mail-pd0-f181.google.com with SMTP id v10so29960865pde.40 for ; Tue, 06 Jan 2015 00:09:48 -0800 (PST) Received: from lgemrelse6q.lge.com (LGEMRELSE6Q.lge.com. [156.147.1.121]) by mx.google.com with ESMTP id y13si87729099pde.84.2015.01.06.00.09.46 for ; Tue, 06 Jan 2015 00:09:47 -0800 (PST) Date: Tue, 6 Jan 2015 17:09:48 +0900 From: Joonsoo Kim Subject: Re: [PATCH 1/2] mm/slub: optimize alloc/free fastpath by removing preemption on/off Message-ID: <20150106080948.GA18346@js1304-P5Q-DELUXE> References: <1420421765-3209-1-git-send-email-iamjoonsoo.kim@lge.com> <1420513392.24290.2.camel@stgolabs.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1420513392.24290.2.camel@stgolabs.net> Sender: owner-linux-mm@kvack.org List-ID: To: Davidlohr Bueso Cc: Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jesper Dangaard Brouer , rostedt@goodmis.org, Thomas Gleixner On Mon, Jan 05, 2015 at 07:03:12PM -0800, Davidlohr Bueso wrote: > On Mon, 2015-01-05 at 10:36 +0900, Joonsoo Kim wrote: > > - preempt_disable(); > > - c = this_cpu_ptr(s->cpu_slab); > > + do { > > + tid = this_cpu_read(s->cpu_slab->tid); > > + c = this_cpu_ptr(s->cpu_slab); > > + } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid)); > > + barrier(); > > I don't see the compiler reodering the object/page stores below, since c > is updated in the loop anyway. Is this really necessary (same goes for > slab_free)? The generated code by gcc 4.8 looks correct without it. > Additionally, the implied barriers for preemption control aren't really > the same semantics used here (if that is actually the reason why you are > using them). Hello, I'd like to use tid as a pivot so it should be fetched before fetching anything on c. Is it impossible even if !CONFIG_PREEMPT without barrier()? Thanks. -- 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/ . Don't email: email@kvack.org