From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, TVD_PH_BODY_ACCOUNTS_PRE autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 33A53C11D05 for ; Thu, 20 Feb 2020 08:46:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F051D207FD for ; Thu, 20 Feb 2020 08:46:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b="deUwhqPq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726829AbgBTIqX (ORCPT ); Thu, 20 Feb 2020 03:46:23 -0500 Received: from esa3.hc3370-68.iphmx.com ([216.71.145.155]:19254 "EHLO esa3.hc3370-68.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726501AbgBTIqW (ORCPT ); Thu, 20 Feb 2020 03:46:22 -0500 X-Greylist: delayed 427 seconds by postgrey-1.27 at vger.kernel.org; Thu, 20 Feb 2020 03:46:22 EST DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=citrix.com; s=securemail; t=1582188382; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=JwHl4quXWDG9itkjDYku543f/vfU0gx98KV7jgfEzIs=; b=deUwhqPq14V103UTUp8rLwhZ+mSjnmQ8rHFGKXIkn1HB22dXM9EEfTig RNf1pAFhMnJv2dsF1UVrOXjAyszfVw/E0qwwKWK8iZcO1USzg/ekjgnDb 9Yv1HYp7KLYWy31ulaQZq1icmXdEpBUTlBvSvYWJCLjtc1fmZ8MI6agG1 M=; Authentication-Results: esa3.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none; spf=None smtp.pra=roger.pau@citrix.com; spf=Pass smtp.mailfrom=roger.pau@citrix.com; spf=None smtp.helo=postmaster@mail.citrix.com Received-SPF: None (esa3.hc3370-68.iphmx.com: no sender authenticity information available from domain of roger.pau@citrix.com) identity=pra; client-ip=162.221.158.21; receiver=esa3.hc3370-68.iphmx.com; envelope-from="roger.pau@citrix.com"; x-sender="roger.pau@citrix.com"; x-conformance=sidf_compatible Received-SPF: Pass (esa3.hc3370-68.iphmx.com: domain of roger.pau@citrix.com designates 162.221.158.21 as permitted sender) identity=mailfrom; client-ip=162.221.158.21; receiver=esa3.hc3370-68.iphmx.com; envelope-from="roger.pau@citrix.com"; x-sender="roger.pau@citrix.com"; x-conformance=sidf_compatible; x-record-type="v=spf1"; x-record-text="v=spf1 ip4:209.167.231.154 ip4:178.63.86.133 ip4:195.66.111.40/30 ip4:85.115.9.32/28 ip4:199.102.83.4 ip4:192.28.146.160 ip4:192.28.146.107 ip4:216.52.6.88 ip4:216.52.6.188 ip4:162.221.158.21 ip4:162.221.156.83 ip4:168.245.78.127 ~all" Received-SPF: None (esa3.hc3370-68.iphmx.com: no sender authenticity information available from domain of postmaster@mail.citrix.com) identity=helo; client-ip=162.221.158.21; receiver=esa3.hc3370-68.iphmx.com; envelope-from="roger.pau@citrix.com"; x-sender="postmaster@mail.citrix.com"; x-conformance=sidf_compatible IronPort-SDR: MM0J4GlVDlB8jW19M11+P9HrOGhNxD8WXYL9vu3YBiAQ460tEWfz3gUg2Lw6ArGektClf8Nbag ZDMsNn+bIaHgvmiQrWsOTOXSdwNZIukFIJ+v8ThpcN5voCcqc9fpCjOv1dFXfaPkJlXRiaocNz Ey3nz+5z5gJ8Z3tkNDhfq+2pULZijq4YhGeqIYtykJ4RyOTbAeqOEVpuzrpMAKyUgCJObCNTDs ys4QXG50X3UKLzLY0I+Ya9hAkPZ3tBMhdhqXVkrciAd+JgmZ9nUhR/Mfl0wZ+8MU2oflNLNG06 Zow= X-SBRS: 2.7 X-MesageID: 12723432 X-Ironport-Server: esa3.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.70,463,1574139600"; d="scan'208";a="12723432" Date: Thu, 20 Feb 2020 09:39:04 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Anchal Agarwal CC: , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [RFC PATCH v3 06/12] xen-blkfront: add callbacks for PM suspend and hibernation Message-ID: <20200220083904.GI4679@Air-de-Roger> References: <890c404c585d7790514527f0c021056a7be6e748.1581721799.git.anchalag@amazon.com> <20200217100509.GE4679@Air-de-Roger> <20200217230553.GA8100@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <20200218091611.GN4679@Air-de-Roger> <20200219180424.GA17584@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200219180424.GA17584@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To AMSPEX02CL01.citrite.net (10.69.22.125) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Thanks for this work, please see below. On Wed, Feb 19, 2020 at 06:04:24PM +0000, Anchal Agarwal wrote: > On Tue, Feb 18, 2020 at 10:16:11AM +0100, Roger Pau Monné wrote: > > On Mon, Feb 17, 2020 at 11:05:53PM +0000, Anchal Agarwal wrote: > > > On Mon, Feb 17, 2020 at 11:05:09AM +0100, Roger Pau Monné wrote: > > > > On Fri, Feb 14, 2020 at 11:25:34PM +0000, Anchal Agarwal wrote: > > > > > From: Munehisa Kamata > > > > > > > > > Add freeze, thaw and restore callbacks for PM suspend and hibernation > > > > > support. All frontend drivers that needs to use PM_HIBERNATION/PM_SUSPEND > > > > > events, need to implement these xenbus_driver callbacks. > > > > > The freeze handler stops a block-layer queue and disconnect the > > > > > frontend from the backend while freeing ring_info and associated resources. > > > > > The restore handler re-allocates ring_info and re-connect to the > > > > > backend, so the rest of the kernel can continue to use the block device > > > > > transparently. Also, the handlers are used for both PM suspend and > > > > > hibernation so that we can keep the existing suspend/resume callbacks for > > > > > Xen suspend without modification. Before disconnecting from backend, > > > > > we need to prevent any new IO from being queued and wait for existing > > > > > IO to complete. > > > > > > > > This is different from Xen (xenstore) initiated suspension, as in that > > > > case Linux doesn't flush the rings or disconnects from the backend. > > > Yes, AFAIK in xen initiated suspension backend takes care of it. > > > > No, in Xen initiated suspension backend doesn't take care of flushing > > the rings, the frontend has a shadow copy of the ring contents and it > > re-issues the requests on resume. > > > Yes, I meant suspension in general where both xenstore and backend knows > system is going under suspension and not flushing of rings. backend has no idea the guest is going to be suspended. Backend code is completely agnostic to suspension/resume. > That happens > in frontend when backend indicates that state is closing and so on. > I may have written it in wrong context. I'm afraid I'm not sure I fully understand this last sentence. > > > > > +static int blkfront_freeze(struct xenbus_device *dev) > > > > > +{ > > > > > + unsigned int i; > > > > > + struct blkfront_info *info = dev_get_drvdata(&dev->dev); > > > > > + struct blkfront_ring_info *rinfo; > > > > > + /* This would be reasonable timeout as used in xenbus_dev_shutdown() */ > > > > > + unsigned int timeout = 5 * HZ; > > > > > + int err = 0; > > > > > + > > > > > + info->connected = BLKIF_STATE_FREEZING; > > > > > + > > > > > + blk_mq_freeze_queue(info->rq); > > > > > + blk_mq_quiesce_queue(info->rq); > > > > > + > > > > > + for (i = 0; i < info->nr_rings; i++) { > > > > > + rinfo = &info->rinfo[i]; > > > > > + > > > > > + gnttab_cancel_free_callback(&rinfo->callback); > > > > > + flush_work(&rinfo->work); > > > > > + } > > > > > + > > > > > + /* Kick the backend to disconnect */ > > > > > + xenbus_switch_state(dev, XenbusStateClosing); > > > > > > > > Are you sure this is safe? > > > > > > > In my testing running multiple fio jobs, other test scenarios running > > > a memory loader works fine. I did not came across a scenario that would > > > have failed resume due to blkfront issues unless you can sugest some? > > > > AFAICT you don't wait for the in-flight requests to be finished, and > > just rely on blkback to finish processing those. I'm not sure all > > blkback implementations out there can guarantee that. > > > > The approach used by Xen initiated suspension is to re-issue the > > in-flight requests when resuming. I have to admit I don't think this > > is the best approach, but I would like to keep both the Xen and the PM > > initiated suspension using the same logic, and hence I would request > > that you try to re-use the existing resume logic (blkfront_resume). > > > > > > I don't think you wait for all requests pending on the ring to be > > > > finished by the backend, and hence you might loose requests as the > > > > ones on the ring would not be re-issued by blkfront_restore AFAICT. > > > > > > > AFAIU, blk_mq_freeze_queue/blk_mq_quiesce_queue should take care of no used > > > request on the shared ring. Also, we I want to pause the queue and flush all > > > the pending requests in the shared ring before disconnecting from backend. > > > > Oh, so blk_mq_freeze_queue does wait for in-flight requests to be > > finished. I guess it's fine then. > > > Ok. > > > Quiescing the queue seemed a better option here as we want to make sure ongoing > > > requests dispatches are totally drained. > > > I should accept that some of these notion is borrowed from how nvme freeze/unfreeze > > > is done although its not apple to apple comparison. > > > > That's fine, but I would still like to requests that you use the same > > logic (as much as possible) for both the Xen and the PM initiated > > suspension. > > > > So you either apply this freeze/unfreeze to the Xen suspension (and > > drop the re-issuing of requests on resume) or adapt the same approach > > as the Xen initiated suspension. Keeping two completely different > > approaches to suspension / resume on blkfront is not suitable long > > term. > > > I agree with you on overhaul of xen suspend/resume wrt blkfront is a good > idea however, IMO that is a work for future and this patch series should > not be blocked for it. What do you think? It's not so much that I think an overhaul of suspend/resume in blkfront is needed, it's just that I don't want to have two completely different suspend/resume paths inside blkfront. So from my PoV I think the right solution is to either use the same code (as much as possible) as it's currently used by Xen initiated suspend/resume, or to also switch Xen initiated suspension to use the newly introduced code. Having two different approaches to suspend/resume in the same driver is a recipe for disaster IMO: it adds complexity by forcing developers to take into account two different suspend/resume approaches when there's no need for it. Thanks, Roger.