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 ABE3AC678D5 for ; Tue, 7 Mar 2023 21:05:47 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pZeUF-00088g-Ax; Tue, 07 Mar 2023 16:04:43 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pZeUC-00087s-27 for qemu-devel@nongnu.org; Tue, 07 Mar 2023 16:04:40 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pZeU8-0002hD-EF for qemu-devel@nongnu.org; Tue, 07 Mar 2023 16:04:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678223074; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nR0EVX41VM86kg5849QDlLjUDoJ/9wiGw9aZDX6pxBk=; b=aIp+Fe2JAubq7MkI04sVCB/Ntc6xAPCdOlDORJShJQ+abTT73DgrQmC3llKgPw//rLljUS vH0wTIhVVw6uLf0befq2dsUHLsPNs7X5vpcncKwV8ioeGY+LFXcfqUqduWVeSY0fB4BDew /9wbzaoGRdAbSgsIWYSj44l15RDXuM0= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-292-Af-xbui9Obq4I6K90Y2sug-1; Tue, 07 Mar 2023 16:04:33 -0500 X-MC-Unique: Af-xbui9Obq4I6K90Y2sug-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CF7E91C0A589; Tue, 7 Mar 2023 21:04:32 +0000 (UTC) Received: from localhost (unknown [10.39.192.86]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4A1BD44002; Tue, 7 Mar 2023 21:04:31 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Hanna Reitz , Kevin Wolf , qemu-block@nongnu.org, Emanuele Giuseppe Esposito , Paolo Bonzini , Stefan Hajnoczi Subject: [PATCH v2 1/3] block: make BlockBackend->quiesce_counter atomic Date: Tue, 7 Mar 2023 16:04:25 -0500 Message-Id: <20230307210427.269214-2-stefanha@redhat.com> In-Reply-To: <20230307210427.269214-1-stefanha@redhat.com> References: <20230307210427.269214-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org The main loop thread increments/decrements BlockBackend->quiesce_counter when drained sections begin/end. The counter is read in the I/O code path. Therefore this field is used to communicate between threads without a lock. Acquire/release are not necessary because the BlockBackend->in_flight counter already uses sequentially consistent accesses and running I/O requests hold that counter when blk_wait_while_drained() is called. qatomic_read() can be used. Use qatomic_fetch_inc()/qatomic_fetch_dec() for modifications even though sequentially consistent atomic accesses are not strictly required here. They are, however, nicer to read than multiple calls to qatomic_read() and qatomic_set(). Since beginning and ending drain is not a hot path the extra cost doesn't matter. Signed-off-by: Stefan Hajnoczi --- block/block-backend.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/block/block-backend.c b/block/block-backend.c index 278b04ce69..68807be32b 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -80,7 +80,7 @@ struct BlockBackend { NotifierList remove_bs_notifiers, insert_bs_notifiers; QLIST_HEAD(, BlockBackendAioNotifier) aio_notifiers; - int quiesce_counter; + int quiesce_counter; /* atomic: written under BQL, read by other threads */ CoQueue queued_requests; bool disable_request_queuing; @@ -1057,7 +1057,7 @@ void blk_set_dev_ops(BlockBackend *blk, const BlockDevOps *ops, blk->dev_opaque = opaque; /* Are we currently quiesced? Should we enforce this right now? */ - if (blk->quiesce_counter && ops && ops->drained_begin) { + if (qatomic_read(&blk->quiesce_counter) && ops && ops->drained_begin) { ops->drained_begin(opaque); } } @@ -1271,7 +1271,7 @@ static void coroutine_fn blk_wait_while_drained(BlockBackend *blk) { assert(blk->in_flight > 0); - if (blk->quiesce_counter && !blk->disable_request_queuing) { + if (qatomic_read(&blk->quiesce_counter) && !blk->disable_request_queuing) { blk_dec_in_flight(blk); qemu_co_queue_wait(&blk->queued_requests, NULL); blk_inc_in_flight(blk); @@ -2568,7 +2568,7 @@ static void blk_root_drained_begin(BdrvChild *child) BlockBackend *blk = child->opaque; ThrottleGroupMember *tgm = &blk->public.throttle_group_member; - if (++blk->quiesce_counter == 1) { + if (qatomic_fetch_inc(&blk->quiesce_counter) == 0) { if (blk->dev_ops && blk->dev_ops->drained_begin) { blk->dev_ops->drained_begin(blk->dev_opaque); } @@ -2586,7 +2586,7 @@ static bool blk_root_drained_poll(BdrvChild *child) { BlockBackend *blk = child->opaque; bool busy = false; - assert(blk->quiesce_counter); + assert(qatomic_read(&blk->quiesce_counter)); if (blk->dev_ops && blk->dev_ops->drained_poll) { busy = blk->dev_ops->drained_poll(blk->dev_opaque); @@ -2597,12 +2597,12 @@ static bool blk_root_drained_poll(BdrvChild *child) static void blk_root_drained_end(BdrvChild *child) { BlockBackend *blk = child->opaque; - assert(blk->quiesce_counter); + assert(qatomic_read(&blk->quiesce_counter)); assert(blk->public.throttle_group_member.io_limits_disabled); qatomic_dec(&blk->public.throttle_group_member.io_limits_disabled); - if (--blk->quiesce_counter == 0) { + if (qatomic_fetch_dec(&blk->quiesce_counter) == 1) { if (blk->dev_ops && blk->dev_ops->drained_end) { blk->dev_ops->drained_end(blk->dev_opaque); } -- 2.39.2