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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 AFEF8C43381 for ; Tue, 12 Mar 2019 03:52:46 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6BA7B214AF for ; Tue, 12 Mar 2019 03:52:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6BA7B214AF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 09D3F8E0003; Mon, 11 Mar 2019 23:52:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 04C648E0002; Mon, 11 Mar 2019 23:52:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E7CAB8E0003; Mon, 11 Mar 2019 23:52:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-qt1-f198.google.com (mail-qt1-f198.google.com [209.85.160.198]) by kanga.kvack.org (Postfix) with ESMTP id BB67F8E0002 for ; Mon, 11 Mar 2019 23:52:45 -0400 (EDT) Received: by mail-qt1-f198.google.com with SMTP id 35so1083377qty.12 for ; Mon, 11 Mar 2019 20:52:45 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-original-authentication-results:x-gm-message-state:date:from:to :cc:subject:message-id:references:mime-version:content-disposition :content-transfer-encoding:in-reply-to; bh=E/UyB+xWk/xehLCQmoblfGNsmlWELdfSb6B+opPtGT0=; b=t2tXG1FUoj/rEdZbd+6amNqsu0zrrBvbIFkoc/g4yiE1epVHWq6DxqYNNfA/X9CCX2 6xMqUE9b8eAOlBF5M8Zno7uhRnOYM3pTclDVRgCHXi7UjfMUuUtdfugSPf5+hLAz58Hh ODFyf7ZHeL/lu2+n6+XIIbL//oJPgNnrDuUTXkbfgn677DLX5gx9L1wdm6Q/uCdpM0+q i65N9VCt05egSOZ9mRHfpnElSWA4+MuMyJwUvWiRLCG+l50xo0StYwHRuDFoUaEbu2Ge 5yMcTnz7Leh6kxb04h9yfRGOMu2XuHn7eFgrZKLtudGm/J0RGtcxG7SUNxcMb5KKlAvL SC5Q== X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of mst@redhat.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=mst@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com X-Gm-Message-State: APjAAAXsWbQMd/iLN+WawchJXgtnVI9lD51vb+/aB3UogZDpaTNwcKmw XmyHPJWSP3F0gydf8Q68S2GXOo6Ynm6KTkN7ZUGDB++pqp8TP+NQPLu14YkUB/gu+1Ma99bcfhe FFmoa4ZIn72xYOCUBiCa3TUQe3n4+j3BV9/qPT5cK3ExnPZhzYtGh1lT2JOnoe98vhlhN+p2loF HYm6YKyzdU9MPXQTr699K6EzlyFrN3N5HnzaBEmD4EKaMHE+i4pUgt5dtNgu1F0m4dtcBMbayck h9+MmV4gF41nUpgfQSqoY73nywF+AAY3nKmZVd7x4s7gpPv14XB3z+tKwniQKfUV9WtA6whtOv0 NtJdJAiujQCEOVE+OIKnKNFKMUeQ5CZjQ3xGZHr36AS+ikqHvbtdPrZoede3cjHmIwHvgDg4M4F i X-Received: by 2002:ac8:554d:: with SMTP id o13mr28734893qtr.105.1552362765580; Mon, 11 Mar 2019 20:52:45 -0700 (PDT) X-Received: by 2002:ac8:554d:: with SMTP id o13mr28734873qtr.105.1552362764946; Mon, 11 Mar 2019 20:52:44 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1552362764; cv=none; d=google.com; s=arc-20160816; b=VYqVxAwLF5WKey1b2GPOuqZd+V5qJZddFhvnWQKhmKHeF0Gy70pVmkqkc9qwfI+qK9 j7Cw868vTinTvBa8Y1iU4SrMtE/+Gpgcn6Xm4C/kUDCiSG1M4vm64i3d9vNZkSqb9AJC qRALHW+5HPHtoBmNn9lHzWSqH+hOdaYnkNp9mbnebpbIuIUwbuW1nJThNUE9U7v5X5PA Qv3Tq6gy1X6e6W5kaUsEMb0jDwANTomDvTx/jRtXegUt0L6tSs59D1waGqQme/O99MKA KkPtzWi53baxGw+cs1QLbl3YsvdpuasGq/mLI4OCOvpVL/BCYqN9MEWfC0w+U8TdZkQY 2Lzw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date; bh=E/UyB+xWk/xehLCQmoblfGNsmlWELdfSb6B+opPtGT0=; b=Mdt5sd8ZHazki/KfewU59kZSRG2QNgH8jtwB/RLjXxD8olTirYxu7VCs6F4rhDHnr3 IYnwUPA2Hyqu77ysp4IEK9LVfHQX8e2cG1PURUc4Jk6kUJ+N3F/1FMRjeStkoreSAFLz sGvMkL+YKsRo+0FdHJnRTuXywvoTkUdbLI2FDhtgdHTkiGQBxMu1FZsOCXZcvrPLyc3r AO2lrHRH0LhxDMQBjv7TYmkH8cFlzXuakeq6f/CIOj7icL2eVVxoT3N5mJWrEnh8MBVT XpztTga3jdCCy8cSKINBeRb5kMRCJ+wdam3kZlvAxBLv0oU+SLg0W7TnSm8TCeyEtS6V je1Q== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of mst@redhat.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=mst@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id v185sor3255607qki.67.2019.03.11.20.52.44 for (Google Transport Security); Mon, 11 Mar 2019 20:52:44 -0700 (PDT) Received-SPF: pass (google.com: domain of mst@redhat.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; spf=pass (google.com: domain of mst@redhat.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=mst@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com X-Google-Smtp-Source: APXvYqw6vWNjN7roQr24NYlwA5iXQwWdK6cI38JZZ7g3cWXw6ntcj/yHKj2a9lBFrAD0H1GF5Tax7A== X-Received: by 2002:ae9:c30f:: with SMTP id n15mr4412813qkg.227.1552362764721; Mon, 11 Mar 2019 20:52:44 -0700 (PDT) Received: from redhat.com (pool-173-76-246-42.bstnma.fios.verizon.net. [173.76.246.42]) by smtp.gmail.com with ESMTPSA id o188sm4099469qkd.30.2019.03.11.20.52.43 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 11 Mar 2019 20:52:43 -0700 (PDT) Date: Mon, 11 Mar 2019 23:52:41 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: David Miller , hch@infradead.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, peterx@redhat.com, linux-mm@kvack.org, aarcange@redhat.com, linux-arm-kernel@lists.infradead.org, linux-parisc@vger.kernel.org Subject: Re: [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() Message-ID: <20190311235140-mutt-send-email-mst@kernel.org> References: <20190308141220.GA21082@infradead.org> <56374231-7ba7-0227-8d6d-4d968d71b4d6@redhat.com> <20190311095405-mutt-send-email-mst@kernel.org> <20190311.111413.1140896328197448401.davem@davemloft.net> <6b6dcc4a-2f08-ba67-0423-35787f3b966c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6b6dcc4a-2f08-ba67-0423-35787f3b966c@redhat.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Mar 12, 2019 at 10:59:09AM +0800, Jason Wang wrote: > > On 2019/3/12 上午2:14, David Miller wrote: > > From: "Michael S. Tsirkin" > > Date: Mon, 11 Mar 2019 09:59:28 -0400 > > > > > On Mon, Mar 11, 2019 at 03:13:17PM +0800, Jason Wang wrote: > > > > On 2019/3/8 下午10:12, Christoph Hellwig wrote: > > > > > On Wed, Mar 06, 2019 at 02:18:07AM -0500, Jason Wang wrote: > > > > > > This series tries to access virtqueue metadata through kernel virtual > > > > > > address instead of copy_user() friends since they had too much > > > > > > overheads like checks, spec barriers or even hardware feature > > > > > > toggling. This is done through setup kernel address through vmap() and > > > > > > resigter MMU notifier for invalidation. > > > > > > > > > > > > Test shows about 24% improvement on TX PPS. TCP_STREAM doesn't see > > > > > > obvious improvement. > > > > > How is this going to work for CPUs with virtually tagged caches? > > > > > > > > Anything different that you worry? > > > If caches have virtual tags then kernel and userspace view of memory > > > might not be automatically in sync if they access memory > > > through different virtual addresses. You need to do things like > > > flush_cache_page, probably multiple times. > > "flush_dcache_page()" > > > I get this. Then I think the current set_bit_to_user() is suspicious, we > probably miss a flush_dcache_page() there: > > > static int set_bit_to_user(int nr, void __user *addr) > { >         unsigned long log = (unsigned long)addr; >         struct page *page; >         void *base; >         int bit = nr + (log % PAGE_SIZE) * 8; >         int r; > >         r = get_user_pages_fast(log, 1, 1, &page); >         if (r < 0) >                 return r; >         BUG_ON(r != 1); >         base = kmap_atomic(page); >         set_bit(bit, base); >         kunmap_atomic(base); >         set_page_dirty_lock(page); >         put_page(page); >         return 0; > } > > Thanks I think you are right. The correct fix though is to re-implement it using asm and handling pagefault, not gup. Three atomic ops per bit is way to expensive. -- MST