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[209.132.183.28]) by mx.google.com with ESMTPS id l12si481974qtq.216.2019.03.11.19.59.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Mar 2019 19:59:26 -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 CC3BE307CDF5; Tue, 12 Mar 2019 02:59:25 +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 63C4660C4C; Tue, 12 Mar 2019 02:59:14 +0000 (UTC) Subject: Re: [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() To: 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> From: Jason Wang Message-ID: <6b6dcc4a-2f08-ba67-0423-35787f3b966c@redhat.com> Date: Tue, 12 Mar 2019 10:59:09 +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: <20190311.111413.1140896328197448401.davem@davemloft.net> 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 [10.5.110.49]); Tue, 12 Mar 2019 02:59:26 +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 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