From: "Martin K. Petersen" Subject: Re: [PATCH] Performance Improvement in CRC16 Calculations. Date: Sat, 11 Aug 2018 11:36:20 -0400 Message-ID: References: <1533928331-21303-1-git-send-email-jeff.lien@wdc.com> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, herbert@gondor.apana.org.au, tim.c.chen@linux.intel.com, martin.petersen@oracle.com, david.darrington@wdc.com, jeff.furlong@wdc.com To: Jeff Lien Return-path: In-Reply-To: <1533928331-21303-1-git-send-email-jeff.lien@wdc.com> (Jeff Lien's message of "Fri, 10 Aug 2018 14:12:11 -0500") Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org Jeff, > This patch provides a performance improvement for the CRC16 > calculations done in read/write workloads using the T10 Type 1/2/3 > guard field. For example, today with sequential write workloads (one > thread/CPU of IO) we consume 100% of the CPU because of the CRC16 > computation bottleneck. Today's block devices are considerably > faster, but the CRC16 calculation prevents folks from utilizing the > throughput of such devices. To speed up this calculation and expose > the block device throughput, we slice the old single byte for loop > into a 16 byte for loop, with a larger CRC table to match. The result > has shown 5x performance improvements on various big endian and little > endian systems running the 4.18.0 kernel version. The reason I went with a simple slice-by-one approach was that the larger tables had a negative impact on the CPU caches. So while slice-by-N numbers looked better in synthetic benchmarks, actual application performance started getting affected as the tables grew larger. These days we obviously use the hardware-accelerated CRC calculation so the software table approach mostly serves as a reference implementation. But given your big vs. little endian performance metrics, I'm assuming you guys are focused on embedded processors without support for CRC acceleration? I have no problem providing a choice for bigger tables. My only concern is that the selection heuristics need to be more than one-dimensional. Latency and cache side effects are often more important than throughput. At least on the initiator side. Also, I'd like to keep the original slice-by-one implementation for reference purposes. -- Martin K. Petersen Oracle Linux Engineering