From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965038AbdKCCbD (ORCPT ); Thu, 2 Nov 2017 22:31:03 -0400 Received: from mga14.intel.com ([192.55.52.115]:48178 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964922AbdKCCbC (ORCPT ); Thu, 2 Nov 2017 22:31:02 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,336,1505804400"; d="scan'208";a="1213670416" Subject: Re: [PATCH v2] buffer: Avoid setting buffer bits that are already set To: Jan Kara , Jens Axboe , Darrick J Wong , Eric Biggers , Andreas Gruenbacher , Jeff Layton Cc: Dave , Andi Kleen , Tim Chen , Ying Huang , Aaron Lu , Linux Kernel References: <1508807802-9691-1-git-send-email-kemi.wang@intel.com> From: kemi Message-ID: Date: Fri, 3 Nov 2017 10:29:13 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1508807802-9691-1-git-send-email-kemi.wang@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017年10月24日 09:16, Kemi Wang wrote: > It's expensive to set buffer flags that are already set, because that > causes a costly cache line transition. > > A common case is setting the "verified" flag during ext4 writes. > This patch checks for the flag being set first. > > With the AIM7/creat-clo benchmark testing on a 48G ramdisk based-on ext4 > file system, we see 3.3%(15431->15936) improvement of aim7.jobs-per-min on > a 2-sockets broadwell platform. > > What the benchmark does is: it forks 3000 processes, and each process do > the following: > a) open a new file > b) close the file > c) delete the file > until loop=100*1000 times. > > The original patch is contributed by Andi Kleen. > > Signed-off-by: Andi Kleen > Signed-off-by: Kemi Wang > Tested-by: Kemi Wang > Reviewed-by: Jens Axboe > --- Seems that this patch is still not merged. Anything wrong with that? thanks > include/linux/buffer_head.h | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h > index c8dae55..211d8f5 100644 > --- a/include/linux/buffer_head.h > +++ b/include/linux/buffer_head.h > @@ -80,11 +80,14 @@ struct buffer_head { > /* > * macro tricks to expand the set_buffer_foo(), clear_buffer_foo() > * and buffer_foo() functions. > + * To avoid reset buffer flags that are already set, because that causes > + * a costly cache line transition, check the flag first. > */ > #define BUFFER_FNS(bit, name) \ > static __always_inline void set_buffer_##name(struct buffer_head *bh) \ > { \ > - set_bit(BH_##bit, &(bh)->b_state); \ > + if (!test_bit(BH_##bit, &(bh)->b_state)) \ > + set_bit(BH_##bit, &(bh)->b_state); \ > } \ > static __always_inline void clear_buffer_##name(struct buffer_head *bh) \ > { \ >