Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752601AbbKLIUp (ORCPT ); Thu, 12 Nov 2015 03:20:45 -0500 Received: from mail-yk0-f175.google.com ([209.85.160.175]:34051 "EHLO mail-yk0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750946AbbKLIUm (ORCPT ); Thu, 12 Nov 2015 03:20:42 -0500 MIME-Version: 1.0 In-Reply-To: <20151111181813.GD12236@redhat.com> References: <20151111181813.GD12236@redhat.com> Date: Thu, 12 Nov 2015 16:20:41 +0800 Message-ID: Subject: Re: [PATCH 0/2] Introduce the request handling for dm-crypt From: Baolin Wang To: Mike Snitzer Cc: axboe@kernel.dk, Alasdair G Kergon , dm-devel@redhat.com, neilb@suse.com, linux-raid@vger.kernel.org, jack@suse.cz, Arnd Bergmann , LKML , keith.busch@intel.com, jmoyer@redhat.com, Mark Brown , tj@kernel.org, bart.vanassche@sandisk.com, "Garg, Dinesh" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5249 Lines: 115 On 12 November 2015 at 02:18, Mike Snitzer wrote: > On Wed, Nov 11 2015 at 4:31am -0500, > Baolin Wang wrote: > >> Now the dm-crypt code only implemented the 'based-bio' method to encrypt/ >> decrypt block data, which can only hanle one bio at one time. As we know, >> one bio must use the sequential physical address and it also has a limitation >> of length. Thus it may limit the big block encyrtion/decryption when some >> hardware support the big block data encryption. >> >> This patch series introduc the 'based-request' method to handle the data >> encryption/decryption. One request can contain multiple bios, so it can >> handle big block data to improve the efficiency. > > The duality of bio-based vs request-based code paths in DM core frankly > sucks. So the prospect of polluting dm-crypt with a similar duality is > really _not_ interesting. > > Request-based DM requires more memory reserves per device than bio-based > DM. Also, you cannot stack request-based DM ontop of bio-based devices > (be them DM, MD, etc) so request-based DM's underlying storage stack > gets a lot less interesting with this change. > > That said, it could be that the benefits of supporting both bio-based > and request-based DM in dm-crypt outweigh any overhead/limitations. But > you haven't given any performance data to justify this patchset. > > There needs to be a _really_ compelling benefit to do this. > > Also, FYI, having a big CONFIG knob to switch all of dm-crypt from > bio-based to request-based is _not_ acceptable. Both modes would need > to be supported in parallel. Could easily be that not all devices in a > system will benefit from being request-based. > > Regardless, the risk of this change causing request-based DM to become > more brittle than it already is concerns me. > > But I'm trying to keep an open mind... show me data that real hardware > _really_ benefits and we'll go from there. Again, it needs to be "OMG, > this is amazing!" level performance to warrant any further serious > consideration. Thanks for your suggestion. But let me explain it again. Now for many vendors, they supply the encryption hardware (such as AES engine) to accelerate the encyrtion/decryption speed with handling a big block at one time. So if we want the hardware engine can play the best performance, the size of block handled at one time need to be expanded. But it can only handle one bio at one time for bio based dm-crypt, one bio has a size limitation and one bio's size can't make the hardware engine reach its best performance. So we want to introduce the request based dm-crypt. For request based things, some sequential bios can merged into one request to expand the IO size to be a big block handled by hardware engine at one time. With the hardware acceleration, it can improve the encryption/decryption speed. I think 3 questions need to be clarified. 1. Are there ways of enhancing the dm-crypt bio-based target to overcome this? The focus is the size limitation of one bio, its size can not meet the hardware requirement. But one request can have a big block size with merging multiple bios. So I think the request is the best choice. 2. Would any sort of bio aggregation mechanism help? The request can combined sequential bios by block layer automatically. But for bio aggregation, I think it will be similar to that, why do we need recomplement it again? 3. perforamence data It is just a simple dd test result, and will provide the formal report in future. But from the simple test, we can see the improvement. Hardware environment: Board: beaglebone black processor: AM335x 1GHz ARM Cortex-A8 RAM: 512M Cipher: cbc(aes) with AES hardware engine (1) bio based dm-crypt with hardware accelarate: read 64M command: dd if=/dev/dm-0 of=/dev/null bs=512k count=128 iflag=direct 67108864 bytes (67 MB) copied, 11.6592 s, 5.8 MB/s 67108864 bytes (67 MB) copied, 11.6391 s, 5.8 MB/s 67108864 bytes (67 MB) copied, 11.6296 s, 5.8 MB/s (2) request based dm-crypt with hardware accelarate read 64M command: dd if=/dev/dm-0 of=/dev/null bs=512k count=128 iflag=direct 67108864 bytes (67 MB) copied, 5.16586 s, 13.0 MB/s 67108864 bytes (67 MB) copied, 5.19338 s, 12.9 MB/s 67108864 bytes (67 MB) copied, 5.19169 s, 12.9 MB/s (3) bio based dm-crypt with hardware accelarate write 64M command: dd if=/dev/zero of=/dev/dm-0 bs=512k count=128 iflag=direct 67108864 bytes (67 MB) copied, 13.6852 s, 4.9 MB/s 67108864 bytes (67 MB) copied, 14.0873 s, 4.8 MB/s 67108864 bytes (67 MB) copied, 13.6649 s, 4.9 MB/s (4) request based dm-crypt with hardware accelarate write 64M command: dd if=/dev/zero of=/dev/dm-0 bs=512k count=128 iflag=direct 67108864 bytes (67 MB) copied, 7.27832 s, 9.2 MB/s 67108864 bytes (67 MB) copied, 7.29051 s, 9.2 MB/s 67108864 bytes (67 MB) copied, 7.28318 s, 9.2 MB/s >From the simple result, we can see it at least has a double improvement of the encryption performance. -- Baolin.wang Best Regards -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/