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=-11.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 30604C00A89 for ; Mon, 2 Nov 2020 18:27:45 +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 C2A4922243 for ; Mon, 2 Nov 2020 18:27:44 +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="NLpNCUgx" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C2A4922243 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]:37480 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kZeYR-00039z-Rb for qemu-devel@archiver.kernel.org; Mon, 02 Nov 2020 13:27:43 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:42016) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kZeVr-0008QU-1i for qemu-devel@nongnu.org; Mon, 02 Nov 2020 13:25:03 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:41362) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kZeVp-0007OM-6J for qemu-devel@nongnu.org; Mon, 02 Nov 2020 13:25:02 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604341500; 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=sz2tHExiCaTwr7JNj8W9VMc3FH9XKSMf0xQ8qFGNOu4=; b=NLpNCUgxSwRF/Y3zrjT6zI+hwii8rxgFsS772TIj0rq8advUTz+Xk3K4d570fUaDI7tIk6 8UkqMyBFHrzKh0uCRPQGLAsVmEcHOPvTlfEMcOhkx/E/mbqwlSQ83aiUikPfklHHLyyxsS ++DhpKwMp5KprnAjExSMQeKglW8+J9s= 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-574-y0XfeFFyN9O4O4M51VpHpA-1; Mon, 02 Nov 2020 13:24:56 -0500 X-MC-Unique: y0XfeFFyN9O4O4M51VpHpA-1 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 4924C1006C8D; Mon, 2 Nov 2020 18:24:55 +0000 (UTC) Received: from work-vm (ovpn-114-142.ams2.redhat.com [10.36.114.142]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4442C68431; Mon, 2 Nov 2020 18:24:50 +0000 (UTC) Date: Mon, 2 Nov 2020 18:24:48 +0000 From: "Dr. David Alan Gilbert" To: Peter Xu Subject: Re: [PATCH 2/2] migration: Postpone the kick of the fault thread after recover Message-ID: <20201102182448.GL3673@work-vm> References: <20201102153010.11979-1-peterx@redhat.com> <20201102153010.11979-3-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201102153010.11979-3-peterx@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@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=63.128.21.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/02 03:02:24 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_H5=0.001, RCVD_IN_MSPIKE_WL=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: Peter Maydell , Christian Schoenebeck , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Xu (peterx@redhat.com) wrote: > The new migrate_send_rp_req_pages_pending() call should greatly improve > destination responsiveness because it will resync faulted address after > postcopy recovery. However it is also the 1st place to initiate the page > request from the main thread. > > One thing is overlooked on that migrate_send_rp_message_req_pages() is not > designed to be thread-safe. So if we wake the fault thread before syncing all > the faulted pages in the main thread, it means they can race. > > Postpone the wake up operation after the sync of faulted addresses. > > Fixes: 0c26781c09 ("migration: Sync requested pages after postcopy recovery") > Tested-by: Christian Schoenebeck > Signed-off-by: Peter Xu Reviewed-by: Dr. David Alan Gilbert > --- > migration/savevm.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/migration/savevm.c b/migration/savevm.c > index e8834991ec..5f937a2762 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -2069,12 +2069,9 @@ static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis) > > /* > * This means source VM is ready to resume the postcopy migration. > - * It's time to switch state and release the fault thread to > - * continue service page faults. > */ > migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_RECOVER, > MIGRATION_STATUS_POSTCOPY_ACTIVE); > - qemu_sem_post(&mis->postcopy_pause_sem_fault); > > trace_loadvm_postcopy_handle_resume(); > > @@ -2095,6 +2092,14 @@ static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis) > */ > migrate_send_rp_req_pages_pending(mis); > > + /* > + * It's time to switch state and release the fault thread to continue > + * service page faults. Note that this should be explicitly after the > + * above call to migrate_send_rp_req_pages_pending(). In short: > + * migrate_send_rp_message_req_pages() is not thread safe, yet. > + */ > + qemu_sem_post(&mis->postcopy_pause_sem_fault); > + > return 0; > } > > -- > 2.26.2 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK