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=-11.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 309B2C2D0E2 for ; Tue, 22 Sep 2020 12:11:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC76F2396D for ; Tue, 22 Sep 2020 12:11:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="jaFs8q2x" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726541AbgIVMLg (ORCPT ); Tue, 22 Sep 2020 08:11:36 -0400 Received: from mx2.suse.de ([195.135.220.15]:50162 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726505AbgIVMLf (ORCPT ); Tue, 22 Sep 2020 08:11:35 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1600776693; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5SAy2ca2q3L9EB+unO167nKo1fIg4hrYmsfk4Zg1pow=; b=jaFs8q2xDCD9SVtqdDERHGzFf/DLQqfUWQxyKAdZtU46tzLG3E0u0MuYOIWseAzbuZ0vGO asz2z7MgJtLCrXknt9zxubRAGffXzHd9ctK6Dh8ffDARFZH8nI+BwA1bw04Pt4FN0KwjXy 6RhgSwWDPoMWaJky8MiX4GqGKwhIpNA= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 584FCB330; Tue, 22 Sep 2020 12:12:10 +0000 (UTC) Subject: Re: [PATCH v2 2/3] xen-blkfront: add a parameter for disabling of persistent grants To: SeongJae Park , konrad.wilk@oracle.com, roger.pau@citrix.com Cc: SeongJae Park , axboe@kernel.dk, aliguori@amazon.com, amit@kernel.org, mheyne@amazon.de, pdurrant@amazon.co.uk, linux-block@vger.kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org References: <20200922105209.5284-1-sjpark@amazon.com> <20200922105209.5284-3-sjpark@amazon.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: Date: Tue, 22 Sep 2020 14:11:32 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200922105209.5284-3-sjpark@amazon.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 22.09.20 12:52, SeongJae Park wrote: > From: SeongJae Park > > Persistent grants feature provides high scalability. On some small > systems, however, it could incur data copy overheads[1] and thus it is > required to be disabled. It can be disabled from blkback side using a > module parameter, 'feature_persistent'. But, it is impossible from > blkfront side. For the reason, this commit adds a blkfront module > parameter for disabling of the feature. > > [1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability > > Signed-off-by: SeongJae Park > --- > .../ABI/testing/sysfs-driver-xen-blkfront | 9 ++++++ > drivers/block/xen-blkfront.c | 28 +++++++++++++------ > 2 files changed, 29 insertions(+), 8 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkfront b/Documentation/ABI/testing/sysfs-driver-xen-blkfront > index c0a6cb7eb314..9c31334cb2e6 100644 > --- a/Documentation/ABI/testing/sysfs-driver-xen-blkfront > +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkfront > @@ -8,3 +8,12 @@ Description: > is 32 - higher value means more potential throughput but more > memory usage. The backend picks the minimum of the frontend > and its default backend value. > + > +What: /sys/module/xen_blkfront/parameters/feature_persistent > +Date: September 2020 > +KernelVersion: 5.10 > +Contact: SeongJae Park > +Description: > + Whether to enable the persistent grants feature or not. Note > + that this option only takes effect on newly created frontends. > + The default is Y (enable). > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c > index 91de2e0755ae..49c324f377de 100644 > --- a/drivers/block/xen-blkfront.c > +++ b/drivers/block/xen-blkfront.c > @@ -149,6 +149,13 @@ static unsigned int xen_blkif_max_ring_order; > module_param_named(max_ring_page_order, xen_blkif_max_ring_order, int, 0444); > MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the shared ring"); > > +/* Enable the persistent grants feature. */ > +static bool feature_persistent = true; > +module_param(feature_persistent, bool, 0644); > +MODULE_PARM_DESC(feature_persistent, > + "Enables the persistent grants feature"); > + > + > #define BLK_RING_SIZE(info) \ > __CONST_RING_SIZE(blkif, XEN_PAGE_SIZE * (info)->nr_ring_pages) > > @@ -1866,11 +1873,13 @@ static int talk_to_blkback(struct xenbus_device *dev, > message = "writing protocol"; > goto abort_transaction; > } > - err = xenbus_printf(xbt, dev->nodename, > - "feature-persistent", "%u", 1); > - if (err) > - dev_warn(&dev->dev, > - "writing persistent grants feature to xenbus"); > + if (feature_persistent) { > + err = xenbus_printf(xbt, dev->nodename, > + "feature-persistent", "%u", 1); > + if (err) > + dev_warn(&dev->dev, > + "writing persistent grants feature to xenbus"); > + } > > err = xenbus_transaction_end(xbt, 0); > if (err) { > @@ -2316,9 +2325,12 @@ static void blkfront_gather_backend_features(struct blkfront_info *info) > if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0)) > blkfront_setup_discard(info); > > - info->feature_persistent = > - !!xenbus_read_unsigned(info->xbdev->otherend, > - "feature-persistent", 0); > + if (feature_persistent) > + info->feature_persistent = > + !!xenbus_read_unsigned(info->xbdev->otherend, > + "feature-persistent", 0); > + else > + info->feature_persistent = 0; > > indirect_segments = xenbus_read_unsigned(info->xbdev->otherend, > "feature-max-indirect-segments", 0); > Here you have the same problem as in blkback: feature_persistent could change its value between the two tests. Juergen