Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965655Ab2JaUcl (ORCPT ); Wed, 31 Oct 2012 16:32:41 -0400 Received: from www84.your-server.de ([213.133.104.84]:37606 "EHLO www84.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932542Ab2JaUck (ORCPT ); Wed, 31 Oct 2012 16:32:40 -0400 Message-ID: <1351715514.23980.7.camel@wall-e> Subject: Re: [PATCH 1/2] kfifo: round up the fifo size power of 2 From: Stefani Seibold To: Yuanhan Liu Cc: Andrew Morton , linux-kernel@vger.kernel.org Date: Wed, 31 Oct 2012 21:31:54 +0100 In-Reply-To: <20121031064940.GD29509@yliu-dev.sh.intel.com> References: <1351238218-22648-1-git-send-email-yuanhan.liu@linux.intel.com> <20121029135935.bb8b0b2a.akpm@linux-foundation.org> <20121031055916.GC29509@yliu-dev.sh.intel.com> <1351665033.23165.6.camel@wall-e> <20121031064940.GD29509@yliu-dev.sh.intel.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.4.4 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Authenticated-Sender: stefani@seibold.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2342 Lines: 64 Am Mittwoch, den 31.10.2012, 14:49 +0800 schrieb Yuanhan Liu: > On Wed, Oct 31, 2012 at 07:30:33AM +0100, Stefani Seibold wrote: > > Am Mittwoch, den 31.10.2012, 13:59 +0800 schrieb Yuanhan Liu: > > > On Mon, Oct 29, 2012 at 01:59:35PM -0700, Andrew Morton wrote: > > > > On Fri, 26 Oct 2012 15:56:57 +0800 > > > > Yuanhan Liu wrote: > > > > > > > > > Say, if we want to allocate a filo with size of 6 bytes, it would be safer > > > > > to allocate 8 bytes instead of 4 bytes. > > > > > > > > > > ... > > > > > if (!is_power_of_2(size)) > > > > > - size = rounddown_pow_of_two(size); > > > > > + size = roundup_pow_of_two(size); > > > > > > > > > > fifo->in = 0; > > > > > fifo->out = 0; > > > > > > > > hm, well, if the user asked for a 100-element fifo then it is a bit > > > > strange and unexpected to give them a 128-element one. > > > > > > > > > Yes, and I guess the same to give them a 64-element one. > > > > > > > > > > > If there's absolutely no prospect that the kfifo code will ever support > > > > 100-byte fifos then I guess we should rework the API so that the caller > > > > has to pass in log2 of the size, not the size itself. That way there > > > > will be no surprises and no mistakes. > > > > > > > > That being said, the power-of-2 limitation isn't at all intrinsic to a > > > > fifo, so we shouldn't do this. Ideally, we'd change the kfifo > > > > implementation so it does what the caller asked it to do! > > > > > > I'm fine with removing the power-of-2 limitation. Stefani, what's your > > > comment on that? > > > > > > > > You can't remove the power-of-2-limitation, since this would result in a > > performance decrease (bit wise and vs. modulo operation). > > Right. > > > > > Andrew is right, this is an API miss design. So it would be good to > > rework the kfifo_init () and kfifo_alloc() to pass in log2 of the size, > > not the size itself. > > Yes, this would make this issue gone completely. Would you mind to let > me do that? > Yes, do it. It would give as the best results. Greetings, Stefani -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/