From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755561Ab3KEVuJ (ORCPT ); Tue, 5 Nov 2013 16:50:09 -0500 Received: from mga14.intel.com ([143.182.124.37]:59771 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755167Ab3KEVuI (ORCPT ); Tue, 5 Nov 2013 16:50:08 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.93,641,1378882800"; d="scan'208";a="422792173" Message-ID: <52796916.3010703@linux.intel.com> Date: Tue, 05 Nov 2013 13:54:30 -0800 From: David Cohen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131005 Icedove/17.0.9 MIME-Version: 1.0 To: Alan Stern CC: balbi@ti.com, gregkh@linuxfoundation.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/4] usb: gadget: add quirk_ep_out_aligned_size field to struct usb_gadget References: <52793566.9080704@linux.intel.com> In-Reply-To: <52793566.9080704@linux.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/05/2013 10:13 AM, David Cohen wrote: > On 11/05/2013 07:41 AM, Alan Stern wrote: >> On Tue, 5 Nov 2013, David Cohen wrote: >> >>>>> +static inline size_t usb_ep_align_maxpacketsize(struct usb_ep *ep, size_t len) >>>>> +{ >>>>> + int aligned; >>>>> + >>>>> + if (ep->desc->bmAttributes & USB_ENDPOINT_XFER_INT) >>>>> + /* >>>>> + * Interrupt eps don't need max packet size to be power of 2, >>>>> + * so can't use cheap IS_ALIGNED() macro. >>>>> + */ >>>>> + aligned = !(len % ep->desc->wMaxPacketSize); >>>>> + else >>>>> + aligned = IS_ALIGNED(len, ep->desc->wMaxPacketSize); >>>> >>>> This isn't on a hot path, and I suspect that the extra "if" will >>>> require nearly as much time as you save by not doing the division. You >>>> might as well always use the % operation. >>> >>> Perhaps if I use unlikely() on 'if' condition instead? >>> Anyway I'll double check the costs of if + IS_ALIGNED vs modulo. >> >> You're missing the point. You and I (not to mention anybody who ever >> reads this code in the future) have already wasted more time talking >> about it and trying to understand it than you will ever save by using >> IS_ALIGNED. >> >> The difference to the computer is minimal at best. Make things easier >> for the programmers. > > I don't see it as complex :) > But I'm fine with your proposal. I can send new patch dropping > IS_ALIGNED() case. At a second though, it's even better to drop both 'if' cases. I can just return round_up(...) directly. Br, David