From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753183AbaIWGDv (ORCPT ); Tue, 23 Sep 2014 02:03:51 -0400 Received: from mail-qg0-f41.google.com ([209.85.192.41]:51174 "EHLO mail-qg0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750712AbaIWGDu (ORCPT ); Tue, 23 Sep 2014 02:03:50 -0400 Date: Tue, 23 Sep 2014 02:03:46 -0400 From: Tejun Heo To: Christoph Hellwig Cc: Jens Axboe , linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org Subject: Re: boot stall regression due to blk-mq: use percpu_ref for mq usage count Message-ID: <20140923060346.GG11740@mtj.dyndns.org> References: <20140919113815.GA10791@lst.de> <541C8047.80705@kernel.dk> <20140923055554.GA10189@lst.de> <20140923055648.GD11740@mtj.dyndns.org> <20140923055924.GA10295@lst.de> <20140923060141.GF11740@mtj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140923060141.GF11740@mtj.dyndns.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 23, 2014 at 02:01:41AM -0400, Tejun Heo wrote: > On Tue, Sep 23, 2014 at 07:59:24AM +0200, Christoph Hellwig wrote: > > "[PATCHSET percpu/for-3.18] percpu_ref: implement switch_to_atomic/percpu()" > > > > looks way to big for 3.17, and the regression was introduced in the 3.17 > > merge window. I'm not sure what was broken before, but it defintively > > survived a lot of testing. > > Do we even care about fixing it for 3.17? scsi-mq isn't enabled by > default even for 3.18. The open-coded percpu ref thing was subtly > broken there. It'd be difficult to trigger but I'm fairly sure it'd > crap out in the wild once in a blue moon. Hmmm... also, this is actually an issue with scsi that block layer is working around. For other drivers (virtio), the latency during shutdown should be completely fine. -- tejun