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 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 AB345C433EF for ; Mon, 13 Sep 2021 12:42:29 +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 5021460FBF for ; Mon, 13 Sep 2021 12:42:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5021460FBF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:53066 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mPlI4-0003Ug-Gq for qemu-devel@archiver.kernel.org; Mon, 13 Sep 2021 08:42:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50448) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mPlBr-0003Jm-SI for qemu-devel@nongnu.org; Mon, 13 Sep 2021 08:36:03 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23001) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mPlBn-0006Px-DX for qemu-devel@nongnu.org; Mon, 13 Sep 2021 08:36:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631536557; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=j4wk6oTRdaTMpnJ1KQmxYj+PhEmuj/KyBemEY058vlA=; b=A6HoN3Qk/BS5BdhjzCyAeUbEXUVCRxZv76EezNPf//v/gzAllemU5qD/o5yZnsQ3Hpcxyt M1csONGRaaiSn2amfOoMhQcxGresEiFckSm/yvU2OH8ttrBWK+2J5eUDK0qfT1di8aeQWz bWAsW20njFJV/UsfW8+xEeFWgsG/JNw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-141-6ESxpX6nMy6AP7Z_rWE30A-1; Mon, 13 Sep 2021 08:35:55 -0400 X-MC-Unique: 6ESxpX6nMy6AP7Z_rWE30A-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 55CBC1084681; Mon, 13 Sep 2021 12:35:54 +0000 (UTC) Received: from localhost (unknown [10.39.195.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id 045C55C1D1; Mon, 13 Sep 2021 12:35:49 +0000 (UTC) Date: Mon, 13 Sep 2021 13:35:48 +0100 From: Stefan Hajnoczi To: John Johnson Subject: Re: [PATCH RFC v2 04/16] vfio-user: connect vfio proxy to remote server Message-ID: References: <924FF1F2-E7AF-4044-B5A4-94A2F1504110@oracle.com> <22CBE2AD-14EB-4162-9E97-FB7D279480AA@oracle.com> <9F0B3728-7F6C-4FBB-BF4C-49F29324F1F5@oracle.com> MIME-Version: 1.0 In-Reply-To: <9F0B3728-7F6C-4FBB-BF4C-49F29324F1F5@oracle.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="K7qwGiUDaxzDJm9i" Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.398, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: Elena Ufimtseva , Jag Raman , Swapnil Ingle , John Levon , QEMU Devel Mailing List , Alex Williamson , "thanos.makatos@nutanix.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --K7qwGiUDaxzDJm9i Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Sep 10, 2021 at 05:25:13AM +0000, John Johnson wrote: >=20 >=20 > > On Sep 8, 2021, at 11:29 PM, Stefan Hajnoczi wrot= e: > >=20 > > On Thu, Sep 09, 2021 at 05:11:49AM +0000, John Johnson wrote: > >>=20 > >>=20 > >> =09I did look at coroutines, but they seemed to work when the sender > >> is triggering the coroutine on send, not when request packets are arri= ving > >> asynchronously to the sends. > >=20 > > This can be done with a receiver coroutine. Its job is to be the only > > thing that reads vfio-user messages from the socket. A receiver > > coroutine reads messages from the socket and wakes up the waiting > > coroutine that yielded from vfio_user_send_recv() or > > vfio_user_pci_process_req(). > >=20 > > (Although vfio_user_pci_process_req() could be called directly from the > > receiver coroutine, it seems safer to have a separate coroutine that > > processes requests so that the receiver isn't blocked in case > > vfio_user_pci_process_req() yields while processing a request.) > >=20 > > Going back to what you mentioned above, the receiver coroutine does > > something like this: > >=20 > > if it's a reply > > reply =3D find_reply(...) > > qemu_coroutine_enter(reply->co) // instead of signalling reply->cv > > else > > QSIMPLEQ_INSERT_TAIL(&pending_reqs, request, next); > > if (pending_reqs_was_empty) { > > qemu_coroutine_enter(process_request_co); > > } > >=20 > > The pending_reqs queue holds incoming requests that the > > process_request_co coroutine processes. > >=20 >=20 >=20 > =09How do coroutines work across threads? There can be multiple vCPU > threads waiting for replies, and I think the receiver coroutine will be > running in the main loop thread. Where would a vCPU block waiting for > a reply? I think coroutine_yield() returns to its coroutine_enter() call= er. A vCPU thread holding the BQL can iterate the event loop if it has reached a synchronous point that needs to wait for a reply before returning. I think we have this situation when a MemoryRegion is accessed on the proxy device. For example, block/block-backend.c:blk_prw() kicks off a coroutine and then runs the event loop until the coroutine finishes: Coroutine *co =3D qemu_coroutine_create(co_entry, &rwco); bdrv_coroutine_enter(blk_bs(blk), co); BDRV_POLL_WHILE(blk_bs(blk), rwco.ret =3D=3D NOT_DONE); BDRV_POLL_WHILE() boils down to a loop like this: while ((cond)) { aio_poll(ctx, true); } I also want to check that I understand the scenarios in which the vfio-user communication code is used: 1. vhost-user-server The vfio-user communication code should run in a given AioContext (it will be the main loop by default but maybe the user will be able to configure a specific IOThread in the future). 2. vCPU thread vfio-user clients The vfio-user communication code is called from the vCPU thread where the proxy device executes. The MemoryRegion->read()/write() callbacks are synchronous, so the thread needs to wait for a vfio-user reply before it can return. Is this what you had in mind? Stefan --K7qwGiUDaxzDJm9i Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmE/RaQACgkQnKSrs4Gr c8jcCAf/SJ3udKtt8/oFj7mmXRHofYWZpEnby06Q5LULQerI5luEdrT1/+R6snw4 wtVDy06LWpN3pZ+I2LqtzoCtAW2suE0Qc3ZZaWlyIs1YOnfGN1WBWgPtp71FT0Li peAXkZbyq/zOKqwPFpPur7xqohtj30hosvmdF/WEfcnBgRGJjTovWO3xQYZK1NRf 7ZFSNnNaGhS4vxYtC4bCiHHiYhjt81OsO0S8B9VyiqVgpA/c3UVcRvErzRmMJLQP Gn0ujOedIVynunbXjutUah143+5wDDUj8Ak17IMKdNdjMaUfEcQMs2SNG7slWwPO hkuAtYfFnEOYlnIPq7Mzl6/el9CEPQ== =Vw/5 -----END PGP SIGNATURE----- --K7qwGiUDaxzDJm9i--