From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755518Ab3KESPo (ORCPT ); Tue, 5 Nov 2013 13:15:44 -0500 Received: from mga02.intel.com ([134.134.136.20]:44707 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755322Ab3KESPm (ORCPT ); Tue, 5 Nov 2013 13:15:42 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.93,535,1378882800"; d="scan'208";a="404036657" Message-ID: <52793566.9080704@linux.intel.com> Date: Tue, 05 Nov 2013 10:13:58 -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: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 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 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. Br, David Cohen