From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 22 Jan 2016 14:56:00 +0000 From: Keith Busch Subject: Re: [BUG] Regression introduced with "block: split bios to max possible length" Message-ID: <20160122145559.GA21984@localhost.localdomain> References: <56A0F1CA.4010303@linux.vnet.ibm.com> <56A14EE4.1020008@fb.com> <20160121225127.GA30993@localhost.localdomain> <20160122032135.GA9244@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Linus Torvalds Cc: Jens Axboe , Stefan Haberland , Linux Kernel Mailing List , linux-s390 , Sebastian Ott List-ID: On Thu, Jan 21, 2016 at 08:15:37PM -0800, Linus Torvalds wrote: > For the case of nvme, for example, I think the max sector number is so > high that you'll never hit that anyway, and you'll only ever hit the > chunk limit. No? The device's max transfer and chunk size are not very large, both fixed at 128KB. We can lose ~70% of potential throughput when IO isn't aligned, and end users reported this when the block layer stopped splitting on alignment for the NVMe drive. So it's a big deal for this h/w, but now I feel awkward defending a device specific feature for the generic block layer. Anyway, the patch was developed with incorrect assumptions. I'd still like to try again after reconciling the queue limit constraints, but I defer to Jens for the near term. Thanks!