From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965548AbbDVQDK (ORCPT ); Wed, 22 Apr 2015 12:03:10 -0400 Received: from mail-qk0-f172.google.com ([209.85.220.172]:35159 "EHLO mail-qk0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965429AbbDVQDD (ORCPT ); Wed, 22 Apr 2015 12:03:03 -0400 Date: Wed, 22 Apr 2015 12:02:58 -0400 From: Tejun Heo To: Peter Zijlstra Cc: Aleksa Sarai , lizefan@huawei.com, mingo@redhat.com, richard@nod.at, fweisbec@gmail.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [PATCH v10 1/4] cgroups: use bitmask to filter for_each_subsys Message-ID: <20150422160258.GE10738@htj.duckdns.org> References: <1429446154-10660-1-git-send-email-cyphar@cyphar.com> <1429446154-10660-2-git-send-email-cyphar@cyphar.com> <20150422152551.GA10738@htj.duckdns.org> <20150422154212.GE3007@worktop.Skamania.guest> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150422154212.GE3007@worktop.Skamania.guest> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey, On Wed, Apr 22, 2015 at 05:42:12PM +0200, Peter Zijlstra wrote: > If, as per the below you want to use the bitmap ops; it needs be > unsigned long. Ah, right. > > > static struct cftype cgroup_dfl_base_files[]; > > > +#define for_each_subsys_which(ss_mask, ss, ssid) \ > > > + for_each_subsys((ss), (ssid)) \ > > > + if ((ss_mask) & (1 << (ssid))) > > > > Maybe using for_each_set_bit() is better? > > > > #define for_each_subsys_which(ss_mask, ss, ssid) \ > > for_each_set_bit(ssid, &(ss_mask), CGROUP_SUBSYS_COUNT) \ > > if ((ss) = group_subsys[ssid] && false) \ > > ; \ > > else > > Clever that ;-) Thanks. It kinda bothers me that for_each_set_bit() doesn't collapse to combo of ffs() + clearing bit off of a temp mask when size is const and <= ulong, which would be quite a bit lighter. Right now it'd be calling into generic find_first/next_bit() functions unconditionally. Ah well, it can be optimized later. -- tejun