From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 D2BE42EAE0; Wed, 6 Nov 2024 15:45:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730907957; cv=none; b=m5Wmslp2iL0qDWnGMu43X+RsSMehkBGlZhlbBoM1UhCHKW0CXmGKtdjVxTAtqJ3FMCooAJuRa3tV6KeP6b3iqT4BYQ3bCiGZc8zWCFCvzsWaWhzOWUdxNigUwiKBTtKjKfExlkdnYHmcSd1tpMvTdXeDNwkwl8hod1NX1yadC+8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730907957; c=relaxed/simple; bh=vwmdwh9p0MkC8M3txKwd05mOaAC7dFJH8WNu6iNevo4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=i98KLOcD/vTfMX6B+oixeanA4l2nTgONvghZVc/fHiSiUhHh4Ym38TFdXmV5QsqiIUGA/fAMyO8p1VQHpBwT8cHGTZIqtx1Xrh2zHVlh8SHETNkUyH1QqNsvY2/moNAIqa9ql7y+d2JKdqVkL/03T59Wmdhltp57fN8CmIfeN+8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=fXeG2DLl; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="fXeG2DLl" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=wyQu6vowSRFmkW1quebGYzpajWeL2fiYU3+PvoZUQlc=; b=fXeG2DLl+Aq9S30LzjI6tdZM5n 4y/6TXuliWDLEehkumnvXwWbUAhv7eF32g/m053D7wJ209SiuwkYhdKNKyzEKzB7lbU66cFIk0qaI K9VoLrViDgxfDDtVGJFfDa6gUIRQtO4qKGW0gLpVlseY1TnQSUwCLzQunwp0sW2uokQFY35EKjz7/ 4S3qm/vPZPqNT8bNrXm9KDvxfBDFBxV8N+XanRpP+3zJqis6hlE7VDaJsUiEDbBy+7DdI3JKJCbWb zoBplHJ9Qco6SphCd/PQqOaE01ahPruhJoOAyWbVnQTDL9otD8pPsF4lSdJdD1Y9UxDLAkcj/nzp2 hyiukz1g==; Received: from hch by bombadil.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1t8iEC-00000003sNS-1QqQ; Wed, 06 Nov 2024 15:45:52 +0000 Date: Wed, 6 Nov 2024 07:45:52 -0800 From: Christoph Hellwig To: Srujana Challa Cc: Christoph Hellwig , "Michael S. Tsirkin" , "virtualization@lists.linux.dev" , "kvm@vger.kernel.org" , "jasowang@redhat.com" , "eperezma@redhat.com" , Nithin Kumar Dabilpuram , Jerin Jacob , Greg Kroah-Hartman Subject: Re: [EXTERNAL] Re: [PATCH v2 0/2] vhost-vdpa: Add support for NO-IOMMU mode Message-ID: References: <20241016134127-mutt-send-email-mst@kernel.org> <20241019201059-mutt-send-email-mst@kernel.org> <20241023041739-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Wed, Nov 06, 2024 at 12:38:02PM +0000, Srujana Challa wrote: > It is going in circles, let me give the summary, > Issue: We need to address the lack of no-IOMMU support in the vhost vDPA driver for better performance. > Measured Performance: On the machine "13th Gen Intel(R) Core(TM) i9-13900K, 32 Cores", we observed Looks ike you are going in circles indeed. Lack of performance is never a reason to disable the basic memoy safety for userspace drivers. The (also quite bad) reason why vfio-nummu was added was to support hardware entirely with an iommu. There is absolutely no reason to add krnel code for new methods of unsafer userspace I/O without an IOMMU ever.