From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga06-in.huawei.com (szxga06-in.huawei.com [45.249.212.32]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B83C92076CB; Wed, 16 Oct 2024 11:37:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.32 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729078633; cv=none; b=XoQnZJYFVaIxSzGJfyeflYGSSAKWfA0MtjogE0EynmEV5IiFFLAniHdPT3uXS//RJ0iifGfjlbFjmQUM7PIURpAqVKq9jYnhEBWpAG1rjmbzpB7an7tphQuT9npb7h/cdbzEAvmlzIrNqJ7s9SvCbf2iDKLqNUC2Gzu3au43gjs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729078633; c=relaxed/simple; bh=XmT6/qpQYuafRC7vpReyn5bI9r22CRroPgAxEDA1uww=; h=Message-ID:Date:MIME-Version:CC:Subject:To:References:From: In-Reply-To:Content-Type; b=tlu7JxxF3Ib9IPeUVjd4llQfah6h2XnNneYUW5GglZqzlKYyjIcU6xfnDLSZWBW6fqz8ezsnfFuzS+4J9rqsafBXNQIVtL2vTkDsApvxSbaQHdTkp0C88za+QFm0LzGSLytkYU25c5l5GhKR1oTvHPYNvuoaqZUVedb9ckPGFrQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.32 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.163]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4XT8893jccz1xx82; Wed, 16 Oct 2024 19:37:13 +0800 (CST) Received: from kwepemm000007.china.huawei.com (unknown [7.193.23.189]) by mail.maildlp.com (Postfix) with ESMTPS id 9D3EA180042; Wed, 16 Oct 2024 19:37:07 +0800 (CST) Received: from [10.67.120.192] (10.67.120.192) by kwepemm000007.china.huawei.com (7.193.23.189) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.39; Wed, 16 Oct 2024 19:37:06 +0800 Message-ID: <67bf12d3-db22-4344-aaa3-9e40c7a0ea52@huawei.com> Date: Wed, 16 Oct 2024 19:37:05 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird CC: , , , , , , , , , , , Subject: Re: [PATCH net 1/9] net: hns3: default enable tx bounce buffer when smmu enabled To: Jakub Kicinski References: <20241011094521.3008298-1-shaojijie@huawei.com> <20241011094521.3008298-2-shaojijie@huawei.com> <20241015181657.14fe9227@kernel.org> From: Jijie Shao In-Reply-To: <20241015181657.14fe9227@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To kwepemm000007.china.huawei.com (7.193.23.189) on 2024/10/16 9:16, Jakub Kicinski wrote: > On Fri, 11 Oct 2024 17:45:13 +0800 Jijie Shao wrote: >> From: Peiyang Wang >> >> When TX bounce buffer is enabled, dma map is used only when the buffer >> initialized. When spending packages, the driver only do dma sync. To > packages -> packets > >> avoid SMMU prefetch, default enable tx bounce buffer if smmu enabled. > you seem to force it to be enabled, rather than just changing > the default. That is strange. Why not let the user lower the value? > > Also I don't see why this is a fix. Seems like a performance > improvement. The SMMU engine on HIP09 chip has a hardware issue. SMMU pagetable prefetch features may prefetch and use a invalid PTE even the PTE is valid at that time. This will cause the device trigger fake pagefaults. The solution is to avoid prefetching by adding a SYNC command when smmu mapping a iova. But the performance of nic has a sharp drop. Then we do this workaround, always enable tx bounce buffer, avoid mapping/unmapping on TX path. This issue only affects HNS3, so we always enable tx bounce buffer to improve performance. Thanks， Jijie Shao