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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 72F20C2D0E2 for ; Thu, 24 Sep 2020 10:13:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1E08821D24 for ; Thu, 24 Sep 2020 10:13:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b="Il0jhs33" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727379AbgIXKN6 (ORCPT ); Thu, 24 Sep 2020 06:13:58 -0400 Received: from esa4.hc3370-68.iphmx.com ([216.71.155.144]:14279 "EHLO esa4.hc3370-68.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727003AbgIXKN5 (ORCPT ); Thu, 24 Sep 2020 06:13:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=citrix.com; s=securemail; t=1600942437; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=Dxq6kcZuD1yLhz83BdQaDBswf+r7H5Cw763TEiIA5Ks=; b=Il0jhs334bOK10DoEpusXfBPn17ZpuBu0s49b+IO38UC2Nst4woelFBN Kx21FFBQXQm6CKaMhTl9eY64+XmHP8UBVwEasemw82W3dZCh4rVSRUgOv i57VK9S8xsmUxzuN+tTcdIiIiYrWD8zVBU3fP5tPz3t7oOCWdnJvLCdS0 s=; Authentication-Results: esa4.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none IronPort-SDR: aa9Yc5uXsNyZc4a3xJjI0PKxAR/Q972NX44zik2KmyXqKIBIwfskdtuxoCOTkpDzQqtPG5Ik68 mWzavWg3o5Ena2knokLLhk07n2q6itSyIjuGpZBNMC3du2eDTN9uB00bOIIh2lBQEtzJ0KYZrC 806XnxjNuw18wsK3GcVFFzAObva5+PihDMkZ8n3kuZIOl1MVqq6xhCLdv2LRIU4QPsAHgSTzXI dI7U6/tY5qSKfc4zjw+ra9KETYu+azT3zprazSO+RJqQzET1XibyqxZUlS635Pb+nk46w8yis4 J6U= X-SBRS: None X-MesageID: 28460264 X-Ironport-Server: esa4.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.77,297,1596513600"; d="scan'208";a="28460264" Date: Thu, 24 Sep 2020 12:13:44 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Konrad Rzeszutek Wilk CC: SeongJae Park , SeongJae Park , , , , , , , Subject: Re: [PATCH] xen-blkback: add a parameter for disabling of persistent grants Message-ID: <20200924101344.GN19254@Air-de-Roger> References: <20200922070125.27251-1-sjpark@amazon.com> <20200923200930.GB11767@char.us.oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline In-Reply-To: <20200923200930.GB11767@char.us.oracle.com> X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To FTLPEX02CL06.citrite.net (10.13.108.179) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 23, 2020 at 04:09:30PM -0400, Konrad Rzeszutek Wilk wrote: > On Tue, Sep 22, 2020 at 09:01:25AM +0200, SeongJae Park wrote: > > From: SeongJae Park > > > > Persistent grants feature provides high scalability. On some small > > systems, however, it could incur data copy overhead[1] and thus it is > > required to be disabled. But, there is no option to disable it. For > > the reason, this commit adds a module parameter for disabling of the > > feature. > > Would it be better suited to have it per guest? I think having a per-backend policy that could be specified at the toolstack level would be nice, but I see that as a further improvement. Having a global backend domain policy of whether persistent grants are enabled or not seems desirable, and if someone wants even more fine grained control this change is AFAICT not incompatible with a per-backend option anyway. Roger.