From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Dobriyan Subject: Re: [PATCH] unaligned: delete 1-byte accessors Date: Mon, 22 Jul 2019 08:22:44 +0300 Message-ID: <20190722052244.GA4235@avx2> References: <20190721215253.GA18177@avx2> <1563750513.2898.4.camel@HansenPartnership.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <1563750513.2898.4.camel@HansenPartnership.com> Sender: linux-kernel-owner@vger.kernel.org To: James Bottomley Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, axboe@kernel.dk, kvalo@codeaurora.org, john.johansen@canonical.com, linux-arch@vger.kernel.org List-Id: linux-arch.vger.kernel.org On Mon, Jul 22, 2019 at 08:08:33AM +0900, James Bottomley wrote: > On Mon, 2019-07-22 at 00:52 +0300, Alexey Dobriyan wrote: > > Each and every 1-byte access is aligned! > > The design idea of this is for parsing descriptors. We simply chunk up > the describing structure using get_unaligned for everything. The > reason is because a lot of these structures come with reserved areas > which we may make use of later. If we're using get_unaligned for > everything we can simply change a u8 to a u16 in the structure > absorbing the reserved padding. With your change now I'd have to chase > down every byte access and replace it with get_unaligned instead of > simply changing the structure. > > What's the significant advantage of this change that compensates for > the problems the above causes? HW descriptors have fixed endianness, you're supposed to use get_unaligned_be32() and friends. For that matter, drivers/scsi/ has exactly 2 get_unaligned() calls one of which can be changed to get_unaligned_be32(). From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-f68.google.com ([209.85.221.68]:33141 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725773AbfGVFWt (ORCPT ); Mon, 22 Jul 2019 01:22:49 -0400 Date: Mon, 22 Jul 2019 08:22:44 +0300 From: Alexey Dobriyan Subject: Re: [PATCH] unaligned: delete 1-byte accessors Message-ID: <20190722052244.GA4235@avx2> References: <20190721215253.GA18177@avx2> <1563750513.2898.4.camel@HansenPartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1563750513.2898.4.camel@HansenPartnership.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: James Bottomley Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, axboe@kernel.dk, kvalo@codeaurora.org, john.johansen@canonical.com, linux-arch@vger.kernel.org Message-ID: <20190722052244.VOORUp0oIFZqnxbFtDRrGPemRfQqZht8fHaLmROFvWE@z> On Mon, Jul 22, 2019 at 08:08:33AM +0900, James Bottomley wrote: > On Mon, 2019-07-22 at 00:52 +0300, Alexey Dobriyan wrote: > > Each and every 1-byte access is aligned! > > The design idea of this is for parsing descriptors. We simply chunk up > the describing structure using get_unaligned for everything. The > reason is because a lot of these structures come with reserved areas > which we may make use of later. If we're using get_unaligned for > everything we can simply change a u8 to a u16 in the structure > absorbing the reserved padding. With your change now I'd have to chase > down every byte access and replace it with get_unaligned instead of > simply changing the structure. > > What's the significant advantage of this change that compensates for > the problems the above causes? HW descriptors have fixed endianness, you're supposed to use get_unaligned_be32() and friends. For that matter, drivers/scsi/ has exactly 2 get_unaligned() calls one of which can be changed to get_unaligned_be32().