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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 D4AEBC433B4 for ; Thu, 1 Apr 2021 02:11:00 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4CD7C6108F for ; Thu, 1 Apr 2021 02:11:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4CD7C6108F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:59864 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lRmnT-00067S-Ea for qemu-devel@archiver.kernel.org; Wed, 31 Mar 2021 22:10:59 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52914) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lRmko-0004ci-Au; Wed, 31 Mar 2021 22:08:14 -0400 Received: from ozlabs.org ([2401:3900:2:1::2]:56869) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lRmkm-0003H1-14; Wed, 31 Mar 2021 22:08:14 -0400 Received: by ozlabs.org (Postfix, from userid 1007) id 4F9mml1DmLz9sWw; Thu, 1 Apr 2021 13:08:07 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gibson.dropbear.id.au; s=201602; t=1617242887; bh=uimYFeg8tfROgkDe8c2UcRwKeHIYOzuGahA/7H0MExY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=armnbMSVYp5oistihOkj9nqMGlCmZN9nxbaWJkQSYqpKjiJTDZi1RUA5kxrnh523I MvaCB7n+E2pfoxI2uVArmv3pyzJnn5cQLJe4jszmJY70CaZy1vf8+DbnDm1XLfguQc TtI1vw3TpleYldbzbRlD9SyFYhPkyiIcupuY6voo= Date: Thu, 1 Apr 2021 12:31:27 +1100 From: David Gibson To: Igor Mammedov Subject: Re: [PATCH 0/4] DEVICE_NOT_DELETED/DEVICE_UNPLUG_ERROR QAPI events Message-ID: References: <20210312200740.815014-1-danielhb413@gmail.com> <20210330012831.2ce0514c@redhat.com> <20210331114914.50950465@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="yzog+coloFKoWSMx" Content-Disposition: inline In-Reply-To: <20210331114914.50950465@redhat.com> Received-SPF: pass client-ip=2401:3900:2:1::2; envelope-from=dgibson@ozlabs.org; helo=ozlabs.org X-Spam_score_int: -17 X-Spam_score: -1.8 X-Spam_bar: - X-Spam_report: (-1.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-devel@nongnu.org, Daniel Henrique Barboza , groug@kaod.org, armbru@redhat.com, qemu-ppc@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --yzog+coloFKoWSMx Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Mar 31, 2021 at 11:49:14AM +0200, Igor Mammedov wrote: > On Wed, 31 Mar 2021 10:46:49 +1100 > David Gibson wrote: >=20 > > On Tue, Mar 30, 2021 at 01:28:31AM +0200, Igor Mammedov wrote: > > > On Wed, 24 Mar 2021 16:09:59 -0300 > > > Daniel Henrique Barboza wrote: > > > =20 > > > > On 3/23/21 10:40 PM, David Gibson wrote: =20 > > > > > On Tue, Mar 23, 2021 at 02:10:22PM -0300, Daniel Henrique Barboza= wrote: =20 > > > > >> > > > > >> > > > > >> On 3/22/21 10:12 PM, David Gibson wrote: =20 > > > > >>> On Fri, Mar 12, 2021 at 05:07:36PM -0300, Daniel Henrique Barbo= za wrote: =20 > > > > >>>> Hi, > > > > >>>> > > > > >>>> This series adds 2 new QAPI events, DEVICE_NOT_DELETED and > > > > >>>> DEVICE_UNPLUG_ERROR. They were (and are still being) discussed= in [1]. > > > > >>>> > > > > >>>> Patches 1 and 3 are independent of the ppc patches and can be = applied > > > > >>>> separately. Patches 2 and 4 are based on David's ppc-for-6.0 b= ranch and > > > > >>>> are dependent on the QAPI patches. =20 > > > > >>> > > > > >>> Implementation looks fine, but I think there's a bit more to di= scuss > > > > >>> before we can apply. > > > > >>> > > > > >>> I think it would make sense to re-order this and put UNPLUG_ERR= OR > > > > >>> first. Its semantics are clearer, and I think there's a strong= er case > > > > >>> for it. =20 > > > > >> > > > > >> Alright > > > > >> =20 > > > > >>> > > > > >>> I'm a bit less sold on DEVICE_NOT_DELETED, after consideration.= Does > > > > >>> it really tell the user/management anything useful beyond what > > > > >>> receiving neither a DEVICE_DELETED nor a DEVICE_UNPLUG_ERROR do= es? =20 > > > > >> > > > > >> > > > > >> It informs that the hotunplug operation exceed the timeout that = QEMU > > > > >> internals considers adequate, but QEMU can't assert that it was = caused > > > > >> by an error or an unexpected delay. The end result is that the d= evice > > > > >> is not going to be deleted from QMP, so DEVICE_NOT_DELETED. = =20 > > > > >=20 > > > > > Is it, though? I mean, it is with this implementation for papr: > > > > > because we clear the unplug_requested flag, even if the guest lat= er > > > > > tries to complete the unplug, it will fail. > > > > >=20 > > > > > But if I understand what Markus was saying correctly, that might = not > > > > > be possible for all hotplug systems. I believe Markus was sugges= ting > > > > > that DEVICE_NOT_DELETED could just mean that we haven't deleted t= he > > > > > device yet, but it could still happen later. > > > > >=20 > > > > > And in that case, I'm not yet sold on the value of a message that > > > > > essentially just means "Ayup, still dunno what's happening, sorry= ". > > > > > =20 > > > > >> Perhaps we should just be straightforward and create a DEVICE_UN= PLUG_TIMEOUT > > > > >> event. =20 > > > > >=20 > > > > > Hm... what if we added a "reason" field to UNPLUG_ERROR. That co= uld > > > > > be "guest rejected hotplug", or something more specific, in the r= are > > > > > case that the guest has a way of signalling something more specif= ic, > > > > > or "timeout" - but the later *only* to be sent in cases where on = the > > > > > timeout we're able to block any later completion of the unplug (a= s we > > > > > can on papr). =20 > > >=20 > > > Is canceling unplug on timeout documented somewhere (like some spec)?= =20 > >=20 > > Uh.. not as such. In the PAPR model, hotplugs and unplugs are mostly > > guest directed, so the question doesn't really arise. > >=20 > > > If not it might (theoretically) confuse guest when it tries to unplug > > > after timeout and leave guest in some unexpected state. =20 > >=20 > > Possible, but probably not that likely. The mechanism we use to > > "cancel" the hotplugs is that we just fail the hypercalls that the > > guest will need to call to actually complete the hotplug. We also > > fail those in some other situations, and that seems to work. > >=20 > > That said, I no longer think this cancelling on timeout is a good > > idea, since it mismatches what happens on other platforms more than I > > think we need to. > >=20 > > My now preferred approach is to revert the timeout changes, but > > instead allow retries of unplugs to be issued. I think that's just a > > matter of resending the unplug message to the guest, while making it > > otherwise a no-op on the qemu side. >=20 > Yep, all we need to do is notify QEMU user, so it knows that unplug > has failed. Then It can decide on it's own what to do with it and also wh= en. I'm not sure even that makes sense. I mean in the cases that the guest specifically signals failure, then yes, we should definitely notify the user. But for the cases the timeout was covering, I'm not convinced a notification is useful: we *don't* know the unplug has failed, we only suspect it, and I don't see that qemu really has any more information than the user about what the expected time for an unplug should be. > > > > I believe that's already covered by the existing API: > > > >=20 > > > >=20 > > > > +# @DEVICE_UNPLUG_ERROR: > > > > +# > > > > +# Emitted when a device hot unplug error occurs. > > > > +# > > > > +# @device: device name > > > > +# > > > > +# @msg: Informative message > > > >=20 > > > > The 'informative message' would be the reason the event occurred. I= n patch > > > > 4/4, for the memory hotunplug refused by the guest, it is being set= as: > > > >=20 > > > > qapi_error =3D g_strdup_printf("Memory hotunplug rejected by = the guest " > > > > "for device %s", dev->id); > > > > qapi_event_send_device_unplug_error(dev->id, qapi_error); > > > >=20 > > > >=20 > > > >=20 > > > > We could use the same DEVICE_UNPLUG_ERROR event in the CPU hotunplu= g timeout > > > > case (currently on patch 2/4) by just changing 'msg', e.g.: > > > >=20 > > > >=20 > > > > qapi_error =3D g_strdup_printf("CPU hotunplug timeout for dev= ice %s", dev->id); > > > > qapi_event_send_device_unplug_error(dev->id, qapi_error); > > > > =20 > > >=20 > > > lets make everything support ACPI (just kidding). =20 > >=20 > > Heh. If nothing else, doesn't help us with existing guests. > >=20 > > > maybe we can reuse already existing ACPI_DEVICE_OST instead of DEVICE= _UNPLUG_ERROR > > > which sort of does the same thing (and more) but instead of strings u= ses status codes > > > defined by spec. =20 > >=20 > > Hmm. I'm a bit dubious about issuing ACPI messages for a non ACPI > > guest, but maybe that could work. >=20 > May be we can rename it to be ACPI agnostic (though I'm not sure how rena= ming > QAPI interfaces should be done (it might upset libvirt for example)). >=20 > (My point was that ACPI spec had already gone through all the trouble def= ining > status of completion and documenting it. Also libvirt supports this notif= ication. > It looks like worthwhile thing to consider if can somehow reuse it outsid= e of > x86 world) Yeah, that's a fair point. --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. 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