From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milan Broz Subject: Re: [dm-devel] DM-CRYPT: Scale to multiple CPUs v3 Date: Sun, 10 Oct 2010 21:31:30 +0200 Message-ID: <4CB21492.8050101@redhat.com> References: <20101010115941.GA8539@basil.fritz.box> <4CB1B3B9.4030205@redhat.com> <20101010130842.GE8256@basil.fritz.box> <4CB1DD1A.5080906@redhat.com> <20101010162257.GA1272@redhat.com> <20101010170151.GD28828@agk-dp.fab.redhat.com> <20101010174454.GA21681@basil.fritz.box> <20101010181736.GE28828@agk-dp.fab.redhat.com> <20101010185100.GB21681@basil.fritz.box> <20101010190734.GH28828@agk-dp.fab.redhat.com> <20101010191640.GC21681@basil.fritz.box> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20101010191640.GC21681@basil.fritz.box> Sender: linux-kernel-owner@vger.kernel.org To: Andi Kleen Cc: Mike Snitzer , Andi Kleen , device-mapper development , pedrib@gmail.com, linux-kernel@vger.kernel.org List-Id: dm-devel.ids On 10/10/2010 09:16 PM, Andi Kleen wrote: >> Not if in_interrupt is set though? >> + if (per_cpu(io_wq_cpu, cpu) == current && !in_interrupt()) { >> >> What I am missing here? > > The interrupt doesn't block on the task. > > Actually most likely that check isn't needed anyways because > that should not happen, was just pure paranoia from my side. I don't think so. If you run crypto in async mode, you get asynchronous callback (kcryptd_asynnc_done() here). AFAIK this callback is called in interrupt context. This callback decreases pending counter and if it reach zero it calls kcryptd_crypt_write_io_submit() -> kcryptd_queue_io(). You cannot call direct encryption if it is called from async callback, so the IO must be always queued to IO workqueue for later. So the in_interrupt() is IMHO equivalent of async flag and it is properly placed there. But previously, there were threads per device, so if one IO thread blocks, others stacked mappings can continue Now I see possibility for deadlock there because we have one io thread now (assuming that 1 CPU situation Alasdair mentioned). Or is there a mistake in my analysis? > >> >> (And assume there is only 1 CPU too for worst case behaviour, presumably.) > > One per process, previously it was always one per CPU. Nope, one singlethread per crypt device (resp. two: io + crypt). Milan