From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: random call_single_data alignment From: Jens Axboe To: "linux-block@vger.kernel.org" Cc: Huang Ying , Ingo Molnar , Peter Zijlstra References: Message-ID: <3875cde5-a193-6aa6-1f9e-561cc66110f2@kernel.dk> Date: Wed, 20 Dec 2017 12:40:25 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 List-ID: On 12/20/17 12:10 PM, Jens Axboe wrote: > For some reason, commit 966a967116e6 was added to the tree without > CC'ing relevant maintainers, even though it's touching random subsystems. > One example is struct request, a core structure in the block layer. > After this change, struct request grows from 296 to 320 bytes on my > setup. > > Why are we blindly aligning to 32 bytes? The comment says to avoid > it spanning two cache lines - but if that's the case, look at the > actual use case and see if that's actually a problem. For struct > request, it is not. > > Seems to me, this should have been applied in the specific area > where it was needed. Keep struct call_single_data (instead of some > __ version), and just manually align it where it matters. https://marc.info/?l=linux-block&m=151379793913822&w=2 https://marc.info/?l=linux-block&m=151379849914002&w=2 In the future, please CC the relevant folks before making (and committing) changes like that. -- Jens Axboe