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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 38966C55189 for ; Wed, 22 Apr 2020 09:24:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 17838206D9 for ; Wed, 22 Apr 2020 09:24:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="grApRieN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726232AbgDVJYQ (ORCPT ); Wed, 22 Apr 2020 05:24:16 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:51111 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725968AbgDVJYQ (ORCPT ); Wed, 22 Apr 2020 05:24:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587547454; 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=DMhA18q5o54p19fFpaLKF4OTjlHgtCkpRiehNkdmtk0=; b=grApRieNK+OmW+Ph9h2tR9zU0uKExcWmmISzc/RrgOUdVjDeysh8DaWsu+FczjWWILTAPj WIzMeEmSv0ZlCUw1vFqJ3GxVNUuoG4yjZ7fkrmNMYqjutoOIvIUTxPBxLB0L7SPmoT9jIe BuntuwErSvNNbVZzI/ZjHmqtDlZ+J5g= 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-47-bYl2gzczORKSGHhwjavuQw-1; Wed, 22 Apr 2020 05:24:10 -0400 X-MC-Unique: bYl2gzczORKSGHhwjavuQw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1503B8017FC; Wed, 22 Apr 2020 09:24:08 +0000 (UTC) Received: from T590 (ovpn-8-28.pek2.redhat.com [10.72.8.28]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7B2FFB3A8F; Wed, 22 Apr 2020 09:23:56 +0000 (UTC) Date: Wed, 22 Apr 2020 17:23:51 +0800 From: Ming Lei To: Dexuan Cui Cc: "Paul E. McKenney" , Josh Triplett , "Rafael J. Wysocki" , "jejb@linux.ibm.com" , "martin.petersen@oracle.com" , "linux-scsi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "hch@lst.de" , "bvanassche@acm.org" , "hare@suse.de" , Michael Kelley , Long Li , "linux-hyperv@vger.kernel.org" , "wei.liu@kernel.org" , Stephen Hemminger , Haiyang Zhang , KY Srinivasan , "linux-pm@vger.kernel.org" Subject: Re: [PATCH] scsi: storvsc: Fix a panic in the hibernation procedure Message-ID: <20200422092351.GF299948@T590> References: <1587514644-47058-1-git-send-email-decui@microsoft.com> <20200422012814.GB299948@T590> <20200422020134.GC299948@T590> <20200422030807.GK17661@paulmck-ThinkPad-P72> <20200422041629.GE299948@T590> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Wed, Apr 22, 2020 at 04:58:14AM +0000, Dexuan Cui wrote: > > From: Ming Lei > > Sent: Tuesday, April 21, 2020 9:16 PM > > ... > > > > > When we're in storvsc_suspend(), all the userspace processes have been > > > > > frozen and all the file systems have been flushed, and there should not > > > > > be too much I/O from the kernel space, so IMO scsi_host_block() should > > be > > > > > pretty fast here. > > > > > > > > I guess it depends on RCU's implementation, so CC RCU guys. > > > > > > > > Hello Paul & Josh, > > > > > > > > Could you clarify that if sysnchronize_rcu becomes quickly during > > > > system suspend? > > > > > > Once you have all but one CPU offlined, it becomes extremely fast, as > > > in roughly a no-op (which is an idea of Josh's from back in the day). > > > But if there is more than one CPU online, then synchronize_rcu() still > > > takes on the order of several to several tens of jiffies. > > > > > > So, yes, in some portions of system suspend, synchronize_rcu() becomes > > > very fast indeed. > > > > Hi Paul, > > > > Thanks for your clarification. > > > > In system suspend path, device is suspended before > > suspend_disable_secondary_cpus(), > > so I guess synchronize_rcu() is not quick enough even though user space > > processes and some kernel threads are frozen. > > > > Thanks, > > Ming > > storvsc_suspend() -> scsi_host_block() is only called in the hibernation > path, which is not a hot path at all, so IMHO we don't really care if it > takes 10ms or 100ms or even 1s. :-) BTW, in my test, typically the Are you sure the 'we' can cover all users? > scsi_host_block() here takes about 3ms in my 40-vCPU VM. If more LUNs are added, the time should be increased proportionallly, that is why I think scsi_host_block() is bad. Thanks, Ming