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=unavailable 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 3C882C43381 for ; Tue, 12 Mar 2019 07:53:51 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EB2D52173C for ; Tue, 12 Mar 2019 07:53:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB2D52173C 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 876E48E0003; Tue, 12 Mar 2019 03:53:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 823DE8E0002; Tue, 12 Mar 2019 03:53:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6EA7F8E0003; Tue, 12 Mar 2019 03:53:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-qk1-f200.google.com (mail-qk1-f200.google.com [209.85.222.200]) by kanga.kvack.org (Postfix) with ESMTP id 4D6FD8E0002 for ; Tue, 12 Mar 2019 03:53:50 -0400 (EDT) Received: by mail-qk1-f200.google.com with SMTP id b188so1471853qkg.15 for ; Tue, 12 Mar 2019 00:53:50 -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:subject:from :to:cc:references:message-id:date:user-agent:mime-version :in-reply-to:content-transfer-encoding:content-language; bh=Z0aXoxS8rVXL7J6k2kLfOYzZULtUi8/02ywxziW0aKs=; b=akbjdtALfQ8nMZ7hWEjmCxBesLskj1zzxx9PlKa0+cvMOo0h5V6DXty6TS4nzgs7vt hS+UbJWYQzV+3/ti//lxa8X8B90Ae7LYuEED59zWKY7+K3JKBtfS1s4mp7jh8OufozGx j0GLYkbo3Yo16vyeiC5xF0rE6l0IgIEg8lUHrUq1JIB5XmrfeBzxCNRQmgsACnEftpUW x2oWcgX9B8N0ZXgsll4/OCKHV9K78R3uCGH7vcCErKtCju4SZM5thhJpI3HyccIQTYtb huWquH8naPqB4vBSOxxIzHDrW0KTHJtC2MJrbxJDCuvE5VvN8Y9XlZ8zeHQeEywX2uQD x/Ng== X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jasowang@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com X-Gm-Message-State: APjAAAXHnWNj2GQG4tyKjMaTFD7I15RFJS5LF/EeAnYmC6k0fKUd0Ykg xpsPmfeK++wB2aQlvxoKs8J1q3Z4Tugly7+PuljKJUQ3be2Ts5UbwKFhtRs2kpizdbL8LRgnofY Yc7kK4HRe06+zD1mon1NIK7mKmdlUENTUFsyOO0PXSqCe3A90tqVtldlzv7FVOLBesA== X-Received: by 2002:aed:3f82:: with SMTP id s2mr29607156qth.284.1552377230106; Tue, 12 Mar 2019 00:53:50 -0700 (PDT) X-Google-Smtp-Source: APXvYqxQneuG3opF9li1yiNm+FzUNx59NcY6M/QZNMlzwm4Pb09TknRtxe2H/sLk2MBNnFt413rs X-Received: by 2002:aed:3f82:: with SMTP id s2mr29607124qth.284.1552377229423; Tue, 12 Mar 2019 00:53:49 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1552377229; cv=none; d=google.com; s=arc-20160816; b=Eyljvg4hYkZpjvtrSZdGksaC5Xp0SAIsysSuvIokthJWTQ9tKI+VoEtDtnUnhKRCSr ECUmJHj9WyrEb1ayHUaPFrjT6nUGZBzHZLwreq53Weug2fzDzMGCFggKjwGdsYzzJ5UG mE0WQGUDePZhsVp6nkAX7E5YKnqHDQynddvtEts4r0ngwH7pcWMHton9uRdLzlLZhGKq NmouZ1mQ1gTTVWkv+eaKRZml2AGl30U2qmYJD5dw/grXdK7bjrtpF9XK0p/gKEataNGE M0YBg4g8veKQdyTxAdJokOY/tfjISHJFrKRX034/UG7APkYbSBYCBBn3oVFdZrhDc7Mj OUyw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-language:content-transfer-encoding:in-reply-to:mime-version :user-agent:date:message-id:references:cc:to:from:subject; bh=Z0aXoxS8rVXL7J6k2kLfOYzZULtUi8/02ywxziW0aKs=; b=kYtAXTO8G/w/Dd6pE9andyuKsfGs+kslpAGBPoUi8g8mvD5aK0Xi3HqN0GDBIgtzYG WS/rv9X+F7ii+t0L7xHsdmkqwC8YvXC0jM//J7XDrlMHKWON6KcNLjkCReDXvICqGbJU 1kuzZBCvaNfuU0UunK99ARI2u3Me/WuiuVTK9q0mPEj68QOKPTUz3OczKeM+3JNSw/kr pPDa6w4hCrN5KxhL26xIh3zlNU3fxRIL/xuJP9hLszgb9uYQyM2xX6LBmn2WWSuhFFVu qFGpry8urg8rh8rfH6qTwUIFfk+70j+OM9qZzM6yB/t1hmch32J9yOzJGgdRgUGJdk3X pQLQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jasowang@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id k31si334910qvh.70.2019.03.12.00.53.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Mar 2019 00:53:49 -0700 (PDT) Received-SPF: pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jasowang@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com 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 904B987621; Tue, 12 Mar 2019 07:53:48 +0000 (UTC) Received: from [10.72.12.17] (ovpn-12-17.pek2.redhat.com [10.72.12.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id 86C1260CA3; Tue, 12 Mar 2019 07:53:39 +0000 (UTC) Subject: Re: [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() From: Jason Wang To: James Bottomley , David Miller , mst@redhat.com Cc: 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 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> <1552367685.23859.22.camel@HansenPartnership.com> Message-ID: <7f779c16-58d1-dd4f-54cf-a7538d4b6fe4@redhat.com> Date: Tue, 12 Mar 2019 15:53:37 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US 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 [10.5.110.26]); Tue, 12 Mar 2019 07:53:48 +0000 (UTC) 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 2019/3/12 下午3:51, Jason Wang wrote: > > On 2019/3/12 下午1:14, James Bottomley wrote: >> On Tue, 2019-03-12 at 10:59 +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); >> This sequence should be OK.  get_user_pages() contains a flush which >> clears the cache above the user virtual address, so on kmap, the page >> is coherent at the new alias.  On parisc at least, kunmap embodies a >> flush_dcache_page() which pushes any changes in the cache above the >> kernel virtual address back to main memory and makes it coherent again >> for the user alias to pick it up. > > > It would be good if kmap()/kunmap() can do this but looks like we can > not assume this? For example, sparc's flush_dcache_page() Sorry, I meant kunmap_atomic(). Thanks > doesn't do flush_dcache_page(). And bio_copy_data_iter() do > flush_dcache_page() after kunmap_atomic(). > > Thanks > > >> >> James >> >