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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 2188CC433F5 for ; Mon, 7 Feb 2022 17:12:14 +0000 (UTC) Received: from localhost ([::1]:59748 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nH7Yj-00089u-11 for qemu-devel@archiver.kernel.org; Mon, 07 Feb 2022 12:12:13 -0500 Received: from eggs.gnu.org ([209.51.188.92]:56298) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nH7Ga-0001Rl-KD for qemu-devel@nongnu.org; Mon, 07 Feb 2022 11:53:28 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:43800) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nH7GX-0000Bh-GL for qemu-devel@nongnu.org; Mon, 07 Feb 2022 11:53:27 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1644252804; 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=VwYdiq2JCp2LvGcB2AK1zLicMdLE3Rj2pv89cJLlMC0=; b=CKQlf61+jDuOEiqlNu/pD8bw5SqaomOoy0VgXDkMEhXR1IfRrLq3xDS9RSR+FJLnVKx6xN y6QFb0Lo/iII1Avr1Sqh1Dtztzckfn6J2b8bs+3U1TMtfixFPL6Saxc6eqoI54fDcrRxiG 8U3kozdvWS1Zin1PI07OeVsPzPt5ngY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-384-n14Yc-OtM_K-d87nNd-juA-1; Mon, 07 Feb 2022 11:53:21 -0500 X-MC-Unique: n14Yc-OtM_K-d87nNd-juA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3831383DEA6; Mon, 7 Feb 2022 16:53:19 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.223]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 38A4970D5C; Mon, 7 Feb 2022 16:53:14 +0000 (UTC) Date: Mon, 7 Feb 2022 17:53:12 +0100 From: Kevin Wolf To: Paolo Bonzini Subject: Re: [PATCH v6 02/33] include/block/block: split header into I/O and global state API Message-ID: References: <20220121170544.2049944-1-eesposit@redhat.com> <20220121170544.2049944-3-eesposit@redhat.com> <1653fd9d-e1e9-5f32-3bd1-62abecd09601@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , qemu-devel@nongnu.org, "Denis V. Lunev" , Eric Blake , Emanuele Giuseppe Esposito , qemu-block@nongnu.org, Juan Quintela , Daniel Henrique Barboza , Markus Armbruster , Richard Henderson , "Dr. David Alan Gilbert" , Greg Kurz , =?iso-8859-1?Q?C=E9dric?= Le Goater , Stefan Hajnoczi , John Snow , David Gibson , Eduardo Habkost , Vladimir Sementsov-Ogievskiy , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Hanna Reitz , qemu-ppc@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 01.02.2022 um 11:30 hat Paolo Bonzini geschrieben: > On 2/1/22 10:45, Emanuele Giuseppe Esposito wrote: > > > That said, even if they are a different category, I think it makes sense > > > to leave them in the same header file as I/O functions, because I/O > > > functions are locked out between drained_begin and drained_end. > > > > Proposed category description: > > /* > > * "Global OR I/O" API functions. These functions can run without > > * the BQL, but only in one specific iothread/main loop. > > * > > * More specifically, these functions use BDRV_POLL_WHILE(bs), which > > * requires the caller to be either in the main thread and hold > > * the BlockdriverState (bs) AioContext lock, or directly in the > > * home thread that runs the bs AioContext. Calling them from > > * another thread in another AioContext would cause deadlocks. > > * > > * Therefore, these functions are not proper I/O, because they > > * can't run in *any* iothreads, but only in a specific one. > > */ > > > > Functions that will surely go under this category: > > > > BDRV_POLL_WHILE > > bdrv_parent_drained_begin_single > > bdrv_parent_drained_end_single > > bdrv_drain_poll > > bdrv_drained_begin > > bdrv_do_drained_begin_quiesce > > bdrv_subtree_drained_begin > > bdrv_drained_end > > bdrv_drained_end_no_poll > > bdrv_subtree_drained_end > > > > (all generated_co_wrapper) > > bdrv_truncate > > bdrv_check > > bdrv_invalidate_cache > > bdrv_flush > > bdrv_pdiscard > > bdrv_readv_vmstate > > bdrv_writev_vmstate > > > > > > What I am not sure: > > > > * bdrv_drain_all_begin - bdrv_drain_all_end - bdrv_drain_all: these were > > classified as GS, because thay are always called from the main loop. > > Should they go in this new category? > > 1) They look at the list of BDS's, and 2) you can't in general be sure that > all BDS's are in *your* AioContext if you call them from a specific > AioContext. > > So they should be GS. I agree, calling drain_all functions can only work from the main thread, so they are GS. > > * how should I interpret "all the callers of BDRV_POLL_WHILE"? > > Meaning, if I consider also the callers of the callers, we end up > > covering much much more functions. Should I only consider the direct > > callers (ie the above)? > > In general it is safe to make a function GS even if it is potentially "GS or > I/O", because that _reduces_ the number of places you can call it from. > It's likewise safe to make it I/O-only, but probably it makes less sense. Basically, we have a hierarchy of categories where you can always call functions in other categories with less restrictions, but never the opposite direction. 1. Common functions 2. I/O functions 3. I/O or GS functions 4. GS functions So common functions must never call any of the other categories. Global state functions can call functions in any category. And "I/O or GS" functions like BDRV_POLL_WHILE() can be called by other "I/O or GS" or just GS functions, but if it's ever (directly or indirectly) called by an I/O or common function, that would be a bug. Kevin