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=-3.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 A1C3FC432C0 for ; Tue, 19 Nov 2019 15:11:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 78EA12231C for ; Tue, 19 Nov 2019 15:11:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gt5pWSV8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728242AbfKSPL1 (ORCPT ); Tue, 19 Nov 2019 10:11:27 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:57857 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727836AbfKSPL0 (ORCPT ); Tue, 19 Nov 2019 10:11:26 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574176285; 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=9N9IO0/XD+xiSOuz/a6MQLrZktW895fzHFoi9+HvgOo=; b=gt5pWSV8xPm4lOxdvpAjLwyx9/Vv+rw5Bjpy9WY+apnt570ixj0iamRcC/giZR2+vyIsNa P3hmP6SyxPgbl5d+3fplMDVS73f5G1L+zvMg5VWyHb6OVN7tbN0w+h9O7fNLpcY7kuHnGm spHkwxfTaqb8hLuMgsbAkigc4csw3TI= 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-91-37ldGzVCN8O_frxDcRm73g-1; Tue, 19 Nov 2019 10:11:21 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 00370DB61; Tue, 19 Nov 2019 15:11:19 +0000 (UTC) Received: from carbon (ovpn-200-17.brq.redhat.com [10.40.200.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id 36C9A1001B32; Tue, 19 Nov 2019 15:11:10 +0000 (UTC) Date: Tue, 19 Nov 2019 16:11:09 +0100 From: Jesper Dangaard Brouer To: Ilias Apalodimas Cc: Lorenzo Bianconi , netdev@vger.kernel.org, davem@davemloft.net, lorenzo.bianconi@redhat.com, mcroce@redhat.com, jonathan.lemon@gmail.com, brouer@redhat.com Subject: Re: [PATCH v4 net-next 2/3] net: page_pool: add the possibility to sync DMA memory for device Message-ID: <20191119161109.7cd83965@carbon> In-Reply-To: <20191119113336.GA25152@apalos.home> References: <84b90677751f54c1c8d47f4036bce5999982379c.1574083275.git.lorenzo@kernel.org> <20191119122358.12276da4@carbon> <20191119113336.GA25152@apalos.home> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: 37ldGzVCN8O_frxDcRm73g-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, 19 Nov 2019 13:33:36 +0200 Ilias Apalodimas wrote: > > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > > > index dfc2501c35d9..4f9aed7bce5a 100644 > > > --- a/net/core/page_pool.c > > > +++ b/net/core/page_pool.c > > > @@ -47,6 +47,13 @@ static int page_pool_init(struct page_pool *pool, > > > =09 (pool->p.dma_dir !=3D DMA_BIDIRECTIONAL)) > > > =09=09return -EINVAL; > > > =20 > > > +=09/* In order to request DMA-sync-for-device the page needs to > > > +=09 * be mapped > > > +=09 */ > > > +=09if ((pool->p.flags & PP_FLAG_DMA_SYNC_DEV) && > > > +=09 !(pool->p.flags & PP_FLAG_DMA_MAP)) > > > +=09=09return -EINVAL; > > > + =20 > >=20 > > I like that you have moved this check to setup time. > >=20 > > There are two other parameters the DMA_SYNC_DEV depend on: > >=20 > > =09struct page_pool_params pp_params =3D { > > =09=09.order =3D 0, > > -=09=09.flags =3D PP_FLAG_DMA_MAP, > > +=09=09.flags =3D PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV, > > =09=09.pool_size =3D size, > > =09=09.nid =3D cpu_to_node(0), > > =09=09.dev =3D pp->dev->dev.parent, > > =09=09.dma_dir =3D xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE, > > +=09=09.offset =3D pp->rx_offset_correction, > > +=09=09.max_len =3D MVNETA_MAX_RX_BUF_SIZE, > > =09}; > >=20 > > Can you add a check, that .max_len must not be zero. The reason is > > that I can easily see people misconfiguring this. And the effect is > > that the DMA-sync-for-device is essentially disabled, without user > > realizing this. The not-realizing part is really bad, especially > > because bugs that can occur from this are very rare and hard to catch. = =20 >=20 > +1 we sync based on the min() value of those=20 >=20 > >=20 > > I'm up for discussing if there should be a similar check for .offset. > > IMHO we should also check .offset is configured, and then be open to > > remove this check once a driver user want to use offset=3D0. Does the > > mvneta driver already have a use-case for this (in non-XDP mode)? =20 >=20 > Not sure about this, since it does not break anything apart from some > performance hit I don't follow the 'performance hit' comment. This is checked at setup time (page_pool_init), thus it doesn't affect runtime. This is a generic optimization principle that I use a lot. Moving code checks out of fast-path, and instead do more at setup/load-time, or even at shutdown-time (like we do for page_pool e.g. check refcnt invariance). This principle is also heavily used by BPF, that adjust BPF-instructions at load-time. It is core to getting the performance we need for high-speed networking. --=20 Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer