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([2620:15c:2cd:203:5cdc:422c:7b28:ebb5]) by smtp.gmail.com with ESMTPSA id g21-v6sm1040349pgh.82.2018.11.07.08.10.20 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 07 Nov 2018 08:10:20 -0800 (PST) Message-ID: <1541607019.196084.210.camel@acm.org> Subject: Re: [PATCH] block: respect virtual boundary mask in bvecs From: Bart Van Assche To: Sagi Grimberg , Johannes Thumshirn , Jens Axboe Cc: Linux Block Layer Mailinglist , Hannes Reinecke , Linux Kernel Mailinglist , Jan Kara Date: Wed, 07 Nov 2018 08:10:19 -0800 In-Reply-To: <950a7996-e0f7-ff34-04da-47581a9496f0@grimberg.me> References: <20181105102301.9752-1-jthumshirn@suse.de> <950a7996-e0f7-ff34-04da-47581a9496f0@grimberg.me> Content-Type: text/plain; charset="UTF-7" X-Mailer: Evolution 3.26.2-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2018-11-06 at 19:30 -0800, Sagi Grimberg wrote: +AD4 +AD4 +AD4 How about changing that expression into the following to make it easier +AD4 +AD4 +AD4 for the compiler to optimize this code? +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 (offset +AHw (bprv-+AD4-bv+AF8-offset +- bprv-+AD4-bv+AF8-len)) +ACY queue+AF8-virt+AF8-boundary(q) +AD4 +AD4 +AD4 +AD4 Uhm I have to admit I'm not really able to parse the above expression. +AD4 +AD4 Sure GCC will do it but I think it's less readable (at least for me). +AD4 +AD4 Let's see what other's think. +AD4 +AD4 I personally not a huge fan of decoding complicated expressions. But if +AD4 others are fine with it then I am too... What I proposed is not a new pattern. It is a pattern that is already used elsewhere in the Linux kernel. A few examples: From dmabounce.c: /+ACo Figure out if we need to bounce from the DMA mask. +ACo-/ if ((dma+AF8-addr +AHw (dma+AF8-addr +- size - 1)) +ACY +AH4-mask) return 1+ADs From dma-direct.h: if ((addr +AHw (addr +- size - 1)) +ACY +AH4-mask) return 0+ADs Bart.