From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: [PATCH] phylib: add mdio-gpio bus driver (v2) Date: Tue, 28 Oct 2008 16:16:42 +0000 Message-ID: <20081028161642.GL1034@flint.arm.linux.org.uk> References: <20081027105318.21923.24436.stgit@Programuotojas.82-135-208-232.ip.zebra.lt> <20081027143734.GA13565@secretlab.ca> <4906C338.6010300@teltonika.lt> <20081028151755.GA1034@flint.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Paulius Zaleckas , netdev@vger.kernel.org, linux-arm-kernel@lists.arm.linux.org.uk, linux-embedded@vger.kernel.org To: Grant Likely Return-path: Received: from caramon.arm.linux.org.uk ([78.32.30.218]:57460 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753520AbYJ1QQ7 (ORCPT ); Tue, 28 Oct 2008 12:16:59 -0400 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Oct 28, 2008 at 09:30:10AM -0600, Grant Likely wrote: > On Tue, Oct 28, 2008 at 9:17 AM, Russell King - ARM Linux > wrote: > > On Tue, Oct 28, 2008 at 07:08:06AM -0600, Grant Likely wrote: > >> On Tue, Oct 28, 2008 at 1:46 AM, Paulius Zaleckas > >> wrote: > >> > Grant Likely wrote: > >> >> The IRQ array is fixed size. You can add it to the mdio_gpio_info > >> >> structure and then just set the pointer here so that only one kzalloc > >> >> is needed. > >> > > >> > It can be put in mdio_gpio_info, but please note that mdio_gpio_info is > >> > allocated with kzalloc() and irq with kmalloc(), because there is no need > >> > to fill this array with zeros(see below). > >> > >> Adding an additional 32 words to be zeroed in the mdio_gpio_info > >> kzalloc is considerably cheaper than doing an additional kmalloc. > >> Plus, once the array is zeroed it is then in the cache and so the > >> filling it with -1 also becomes cheaper. > > > > Actually no, it doesn't become cheaper. You're making the assumption > > that cache lines are allocated when memory is written to. This isn't > > the case with the vast majority of ARM CPUs. > > Okay, I wasn't aware of that on ARM. > > However it is still true that increasing the size of the kzalloc is > cheaper than doing 2 allocs. Yes, that 'irq' array might as well be part of the same structure.