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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT 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 64772C31E46 for ; Wed, 12 Jun 2019 11:51:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44E1A20665 for ; Wed, 12 Jun 2019 11:51:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730504AbfFLLv0 (ORCPT ); Wed, 12 Jun 2019 07:51:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45984 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726004AbfFLLv0 (ORCPT ); Wed, 12 Jun 2019 07:51:26 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 9F96730917AC; Wed, 12 Jun 2019 11:51:25 +0000 (UTC) Received: from localhost (unknown [10.43.2.57]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3F60D60CCC; Wed, 12 Jun 2019 11:51:22 +0000 (UTC) Date: Wed, 12 Jun 2019 13:51:21 +0200 From: Stanislaw Gruszka To: Lorenzo Bianconi Cc: Lorenzo Bianconi , nbd@nbd.name, kvalo@codeaurora.org, linux-wireless@vger.kernel.org Subject: Re: [PATCH v2 2/2] mt76: usb: do not always copy the first part of received frames Message-ID: <20190612115120.GA3496@redhat.com> References: <2ed0b595a12944a8cfea14e066bcc4fa24f0ba44.1559293385.git.lorenzo@kernel.org> <20190612091036.GB2965@redhat.com> <20190612095302.GD8107@localhost.localdomain> <20190612102502.GB4431@redhat.com> <20190612104921.GF8107@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190612104921.GF8107@localhost.localdomain> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Wed, 12 Jun 2019 11:51:25 +0000 (UTC) Sender: linux-wireless-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Wed, Jun 12, 2019 at 12:49:22PM +0200, Lorenzo Bianconi wrote: > > On Wed, Jun 12, 2019 at 11:53:03AM +0200, Lorenzo Bianconi wrote: > > > > On Fri, May 31, 2019 at 11:38:23AM +0200, Lorenzo Bianconi wrote: > > > > > > [...] > > > > > > > > } > > > > > > > > > > urb->num_sgs = max_t(int, i, urb->num_sgs); > > > > > - urb->transfer_buffer_length = urb->num_sgs * q->buf_size, > > > > > + urb->transfer_buffer_length = urb->num_sgs * data_size; > > > > > sg_init_marker(urb->sg, urb->num_sgs); > > > > > > > > > > return i ? : -ENOMEM; > > > > > @@ -611,8 +611,12 @@ static int mt76u_alloc_rx(struct mt76_dev *dev) > > > > > if (!q->entry) > > > > > return -ENOMEM; > > > > > > > > > > - q->buf_size = dev->usb.sg_en ? MT_RX_BUF_SIZE : PAGE_SIZE; > > > > > + if (dev->usb.sg_en) > > > > > + q->buf_size = MT_BUF_WITH_OVERHEAD(MT_RX_BUF_SIZE); > > > > > > > > I strongly recommend to not doing this. While this should work > > > > in theory creating buffer with size of 2k + some bytes might > > > > trigger various bugs in dma mapping or other low level code. > > > > > > even in practice actually :) > > > > I wouldn't be sure about this. It's not common to have buffers of > > such size and crossing pages boundaries. It really can trigger > > nasty bugs on various IOMMU drivers. > > I was just joking, I mean that it worked in the tests I carried out, but I > agree it can trigger some issues in buggy IOMMU drivers My sense of humor declined quite drastically lastly ;-/ > > > but we can be more cautious since probably copying > > > the first 128B will not make any difference > > > > Not sure if I understand what you mean. > > Please correct me if I am wrong but I think max amsdu rx size is 3839B for > mt76. For the sg_en case this frame will span over multiple sg buffers since > sg buffer size is 2048B (2 sg buffers). Moreover if we do not take into account > skb_shared_info when configuring the sg buffer size we will need to always copy > the first 128B of the first buffer since received len will be set to 2048 and > the following if condition will always fail: > > if (SKB_WITH_OVERHEAD(buf_size) >= MT_DMA_HDR_LEN + len) { > } Ok, that I understand. > > > > And skb_shered_info is needed only in first buffer IIUC. > > > > > > > > Also this patch seems to make first patch unnecessary except for > > > > non sg_en case (in which I think rx AMSDU is broken anyway), > > > > so I would prefer just to apply first patch. > > > > > > I do not think rx AMSDU is broken for non sg_en case since the max rx value > > > allowed should be 3839 IIRC and we alloc one page in this case > > > > If that's the case we should be fine, but then I do not understand > > why we allocate 8*2k buffers for sg_en case, isn't that AP can > > sent AMSDU frame 16k big? > > Sorry I did not get what you mean here, could you please explain? If max RX AMSDU size is 3839B I do not see reason why we allocate MT_SG_MAX_SIZE=8 of MT_RX_BUF_SIZE=2k buffers for sg_en case. I thought the reason is that max AMSDU size is 16kB so it fit into 8 sg buffers of 2k. In other words, for me, looks like either - we can not handle AMSDU for non sg case because we do not allocate big enough buffer or - we can just use one PAGE_SIZE buffer for rx and remove sg buffers for rx completely Do I miss something ? Stanislaw