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=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 E9EACC2D0CE for ; Tue, 21 Jan 2020 11:14:48 +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 B22062253D for ; Tue, 21 Jan 2020 11:14:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="PIB7cP3o" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B22062253D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:51916 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1itrUd-0008Tf-Sm for qemu-devel@archiver.kernel.org; Tue, 21 Jan 2020 06:14:47 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:41464) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1itrQL-0002ob-P9 for qemu-devel@nongnu.org; Tue, 21 Jan 2020 06:10:25 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1itrQH-0005wz-4d for qemu-devel@nongnu.org; Tue, 21 Jan 2020 06:10:21 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:20685 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1itrQG-0005wj-RB for qemu-devel@nongnu.org; Tue, 21 Jan 2020 06:10:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579605016; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Dlx2r4Lt9OwxlG7hdFBMuPSB6sH7+RtiZEcvmhgHU+U=; b=PIB7cP3oJpsk8wbBPq97q4um2lBIHfdvMT3XHHPSFP5GiZh2ey+iuR8GmhYZ+gwl43BYoA KvbUMke57yBY86SWeFpdMLtLj0p9kj4DjOjm8+oom9/zIFqMJ3C6qKIkZlvVE7tBzq/u7b ZiDRktLUxeJTaCBAmog/FzuOmX/ViBs= 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-401-p51x5Ld-NleVafUuIC0Ezw-1; Tue, 21 Jan 2020 06:10:15 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4AD9218A6EC1 for ; Tue, 21 Jan 2020 11:10:14 +0000 (UTC) Received: from redhat.com (ovpn-116-23.ams2.redhat.com [10.36.116.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D525360BE0; Tue, 21 Jan 2020 11:10:13 +0000 (UTC) From: Juan Quintela To: "Dr. David Alan Gilbert" Subject: Re: [PATCH v3 3/5] migration: Don't wait in semaphore for thread we know has finished In-Reply-To: <20200117164556.GO3209@work-vm> (David Alan Gilbert's message of "Fri, 17 Jan 2020 16:45:56 +0000") References: <20200116154616.11569-1-quintela@redhat.com> <20200116154616.11569-4-quintela@redhat.com> <20200117164556.GO3209@work-vm> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) Date: Tue, 21 Jan 2020 12:10:11 +0100 Message-ID: <87sgk9gj58.fsf@secure.laptop> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: p51x5Ld-NleVafUuIC0Ezw-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: , Reply-To: quintela@redhat.com Cc: Laurent Vivier , Paolo Bonzini , Thomas Huth , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" "Dr. David Alan Gilbert" wrote: > * Juan Quintela (quintela@redhat.com) wrote: >> If p->quit is true for any channel, we know that it has finished for >> any reason. So don't wait for it, just continue. >>=20 >> Signed-off-by: Juan Quintela >>=20 >> --- >>=20 >> I could be convinced that the right thing to do in that case is to >> just do a break instead of a continue. Each option has its own >> advantages/disadvantanges. >> --- >> migration/ram.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >>=20 >> diff --git a/migration/ram.c b/migration/ram.c >> index 44ca56e1ea..bc918ef28d 100644 >> --- a/migration/ram.c >> +++ b/migration/ram.c >> @@ -1118,6 +1118,12 @@ static void multifd_send_sync_main(RAMState *rs) >> MultiFDSendParams *p =3D &multifd_send_state->params[i]; >> =20 >> trace_multifd_send_sync_main_wait(p->id); >> + qemu_mutex_lock(&p->mutex); >> + if (p->quit) { >> + qemu_mutex_unlock(&p->mutex); >> + continue; >> + } >> + qemu_mutex_unlock(&p->mutex); > > Why is this needed/helps? > You can't depend on the p->quit happening before the=20 > sem_wait, so the main thread still has to do a post on sem_sync before > the join, even with the addition of the check for p->quit. if we have asked the thread to quit, it is inside posibility that it has already quit, so it is not going to be able to do the ->post() for this sem. if ->quit =3D=3D true, then we know that we are exiting. On _normal_ exit, we know that everything is ok. On cancel/error, we don't really know, it deppends how lucky we are. Later, Juan.