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 6898DC43334 for ; Thu, 9 Jun 2022 18:58:23 +0000 (UTC) Received: from localhost ([::1]:58056 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nzNMM-0000Zh-8p for qemu-devel@archiver.kernel.org; Thu, 09 Jun 2022 14:58:22 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48186) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nzLJk-0000s1-5Q for qemu-devel@nongnu.org; Thu, 09 Jun 2022 12:47:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:36302) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nzLJV-0006UR-V1 for qemu-devel@nongnu.org; Thu, 09 Jun 2022 12:47:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1654793237; 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=7bQ8effnjIEoV/FflvyQHU5ECeV5iaJvsuveUZtQFyw=; b=RhF6KrdMTd2rbKqZeqqtPN5LFQd9+KUbflwavGEWkcQ/gfNfl6LNsOUAvNa16EFG7NSfQy XGIzoDYot4RDcZnfs6PPwXE5F8zxf69rYycuBIhuYThRYA/ezHwasH0zTYs1+ZMIdxb8Xq ArfvyyNTFWOB7hBIj9uvvIdZWatH3Ss= 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-61-aWbcqH1iPCOlAV3E_K5BWw-1; Thu, 09 Jun 2022 12:47:16 -0400 X-MC-Unique: aWbcqH1iPCOlAV3E_K5BWw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B25F9294EDDB; Thu, 9 Jun 2022 16:47:15 +0000 (UTC) Received: from localhost (unknown [10.39.193.205]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6C7202166B26; Thu, 9 Jun 2022 16:47:15 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Hanna Reitz , qemu-stable@nongnu.org, Kevin Wolf , qemu-block@nongnu.org, Stefan Hajnoczi , Stefano Garzarella Subject: [PATCH 2/2] linux-aio: explain why max batch is checked in laio_io_unplug() Date: Thu, 9 Jun 2022 17:47:12 +0100 Message-Id: <20220609164712.1539045-3-stefanha@redhat.com> In-Reply-To: <20220609164712.1539045-1-stefanha@redhat.com> References: <20220609164712.1539045-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" It may not be obvious why laio_io_unplug() checks max batch. I discussed this with Stefano and have added a comment summarizing the reason. Cc: Stefano Garzarella Cc: Kevin Wolf Signed-off-by: Stefan Hajnoczi --- block/linux-aio.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/block/linux-aio.c b/block/linux-aio.c index 6078da7e42..9c2393a2f7 100644 --- a/block/linux-aio.c +++ b/block/linux-aio.c @@ -365,6 +365,12 @@ void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s, assert(s->io_q.plugged); s->io_q.plugged--; + /* + * Why max batch checking is performed here: + * Another BDS may have queued requests with a higher dev_max_batch and + * therefore in_queue could now exceed our dev_max_batch. Re-check the max + * batch so we can honor our device's dev_max_batch. + */ if (s->io_q.in_queue >= laio_max_batch(s, dev_max_batch) || (!s->io_q.plugged && !s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending))) { -- 2.36.1