Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S269162AbUIRIaD (ORCPT ); Sat, 18 Sep 2004 04:30:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S269164AbUIRIaD (ORCPT ); Sat, 18 Sep 2004 04:30:03 -0400 Received: from ns.virtualhost.dk ([195.184.98.160]:29827 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S269162AbUIRI36 (ORCPT ); Sat, 18 Sep 2004 04:29:58 -0400 Date: Sat, 18 Sep 2004 10:29:48 +0200 From: Jens Axboe To: Mike Christie Cc: linux-kernel@vger.kernel.org, wa@almesberger.net Subject: Re: [PATCH] modular io schedulers with online switching, #2 Message-ID: <20040918082944.GA1195@suse.de> References: <20040917094436.GB2911@suse.de> <414AB8D2.2080905@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <414AB8D2.2080905@us.ibm.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1722 Lines: 50 On Fri, Sep 17 2004, Mike Christie wrote: > Jens Axboe wrote > >+void blk_wait_queue_drained(request_queue_t *q) > >+{ > >+ struct request_list *rl = &q->rq; > >+ DEFINE_WAIT(wait); > >+ > >+ set_bit(QUEUE_FLAG_DRAIN, &q->queue_flags); > >+ > >+ prepare_to_wait(&rl->drain, &wait, TASK_UNINTERRUPTIBLE); > >+ do { > >+ spin_lock_irq(q->queue_lock); > >+ if (!rl->count[READ] && !rl->count[WRITE]) { > >+ spin_unlock_irq(q->queue_lock); > >+ break; > >+ } > >+ > >+ __generic_unplug_device(q); > >+ spin_unlock_irq(q->queue_lock); > >+ io_schedule(); > >+ } while (1); > >+ finish_wait(&rl->drain, &wait); > >+} > >+ > > Jens, > > If a driver does not allocate requests through blk_get_request, will the > rl->count[] tests need to be changed or do those drivers need to be > changed? For example, if SCSI insterts a special request into the queue, > then someone swaps the io scheduler with no outstanding normal requests > (so the rl->counts will be zero), could the special request still be in > the queue since it allocated its request using kmalloc (the request is > allocated as part of the scsi command). Yes, we need to eliminate stack and kmalloc'ed requests for this to be completely solid. This is something we have been doing for some time already, now would be a good time to fully complete it. There's no way to block incoming request at ->add_request_fn() time, so we have to do it on merge (first path) or request allocation. -- Jens Axboe - 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/