From: James Bottomley Subject: Re: [RFC 12/12] iscsi-target: Add Makefile/Kconfig and update TCM top level Date: Fri, 04 Mar 2011 11:00:21 -0600 Message-ID: <1299258022.7041.64.camel@mulgrave.site> References: <1299036841-23677-1-git-send-email-nab@linux-iscsi.org> <1299036841-23677-13-git-send-email-nab@linux-iscsi.org> <20110301223251.11c95eed.rdunlap@xenotime.net> <1299101531.5401.313.camel@haakon2.linux-iscsi.org> <20110303141928.GA25256@infradead.org> <1299185905.5401.405.camel@haakon2.linux-iscsi.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Christoph Hellwig , Randy Dunlap , linux-scsi , linux-kernel , linux-crypto@vger.kernel.org To: "Nicholas A. Bellinger" Return-path: In-Reply-To: <1299185905.5401.405.camel@haakon2.linux-iscsi.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On Thu, 2011-03-03 at 12:58 -0800, Nicholas A. Bellinger wrote: > On Thu, 2011-03-03 at 09:19 -0500, Christoph Hellwig wrote: > > On Wed, Mar 02, 2011 at 01:32:11PM -0800, Nicholas A. Bellinger wrote: > > > The kernel code itself that is specific to using the SSE v4.2 > > > instruction for CRC32C offload are using #ifdef CONFIG_X86 stubs in > > > iscsi_target_login.c:iscsi_login_setup_crypto(), and !CONFIG_X86 will > > > default to using the unoptimized 1x8 slicing soft CRC32C code. This > > > particular piece of logic has been tested on powerpc and arm and is > > > funcitoning as expected from the kernel level using the arch independent > > > soft code. > > > > I don't think you need that code at all. The crypto code is structured > > to prefer the optimized implementation if it is present. Just stripping > > the x86-specific code out and always requesting the plain crc32c > > algorithm should give you the optimized one if it is present on your > > system. > > > > Please give it a try. > > > > This is what I originally thought as well, but this ended up not being > the case when the logic was originally coded up. I just tried again > with .38-rc7 on a 5500 series machine and simply stubbing out the > CONFIG_X86 part from iscsi_login_setup_crypto() and calling: > > crypto_alloc_hash("crc32c", 0, CRYPTO_ALG_ASYNC) > > does not automatically load and use crc32c_intel.ko when only requesting > plain crc32c. It sounds like there might be a bug in the crypto layer, so the Linux way is to make it work as intended. It's absolutely not acceptable just to pull other layer workarounds into drivers. > The reason for the extra crypto_alloc_hash("crc32c-intel", ...) call in > iscsi_login_setup_crypto() is to load crc32c_intel.ko on-demand for > cpu_has_xmm4_2 capable machines. > > I should mention this is with the following .config: > > CONFIG_CRYPTO_CRC32C=y > CONFIG_CRYPTO_CRC32C_INTEL=m > > This would seem to indicate that CRC32C_INTEL needs to be compiled in > (or at least manually loaded) for libcypto to use the optimized > instructions when the plain crc32c is called, correct..? That sounds right. There's probably not an autoload for this on recognising sse instructions. James James