Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758541AbaGXB5V (ORCPT ); Wed, 23 Jul 2014 21:57:21 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:52428 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756502AbaGXB5T (ORCPT ); Wed, 23 Jul 2014 21:57:19 -0400 MIME-Version: 1.0 In-Reply-To: <20140723231600.GE17798@lenny.home.zabbo.net> References: <1406156130-15575-1-git-send-email-ming.lei@canonical.com> <1406156130-15575-8-git-send-email-ming.lei@canonical.com> <20140723231600.GE17798@lenny.home.zabbo.net> Date: Thu, 24 Jul 2014 09:57:16 +0800 Message-ID: Subject: Re: [PATCH 7/9] aio: add aio_kernel_() interface From: Ming Lei To: Zach Brown Cc: Jens Axboe , Linux Kernel Mailing List , Andrew Morton , Dave Kleikamp , Benjamin LaHaise , Alexander Viro , Linux FS Devel , "open list:AIO" , Kent Overstreet Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 24, 2014 at 7:16 AM, Zach Brown wrote: > On Thu, Jul 24, 2014 at 06:55:28AM +0800, Ming Lei wrote: >> From: Dave Kleikamp >> >> This adds an interface that lets kernel callers submit aio iocbs without >> going through the user space syscalls. This lets kernel callers avoid >> the management limits and overhead of the context. It will also let us >> integrate aio operations with other kernel apis that the user space >> interface doesn't have access to. >> >> This patch is based on Dave's posts in below links: >> >> https://lkml.org/lkml/2013/10/16/365 >> https://groups.google.com/forum/#!topic/linux.kernel/l7mogGJZoKQ > > This was originally written a billion years ago when dinosaurs roamed > the earth. Also, notably, before Kent and Ben reworked a bunch of the Not so far away, this patch is based on Dave's last version of V9, which was posted in Oct, 2013, :-) > aio core. I'd want them to take a look at this patch to make sure that > it doesn't rely on any assumptions that have changed. Looks I missed to Cc Ken, :-( > >> +/* opcode values not exposed to user space */ >> +enum { >> + IOCB_CMD_READ_ITER = 0x10000, >> + IOCB_CMD_WRITE_ITER = 0x10001, >> +}; > > And I think the consensus was that this isn't good enough. Find a way > to encode the kernel caller ops without polluting the uiocb cmd name > space. That is easy, since the two cmd names are only for kernel AIO, whatever should be OK, but looks I didn't see such comment. > > (I've now come to think that this entire approach of having loop use aio > is misguided and that the way forward is to have dio consume what loop > naturally produces -- bios, blk-mq rqs, whatever -- but I'm on to other Yes, that is what these patches are doing, and actually AIO's model is a good match to driver's interface. Lots of drivers use the asynchronous model(submit, complete, ...). > things these days.) At least, loop can improve its throughput much by kernel AIO without big changes to fs/direct-io(attribute much to ITER_BVEC), and vhost-scsi should benefit from it too. Thanks, -- 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/