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[2620:137:e000::1:9]) by mx.google.com with ESMTPS id o9si1972154wrm.230.2019.03.11.11.14.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Mar 2019 11:14:16 -0700 (PDT) Received-SPF: neutral (google.com: 2620:137:e000::1:9 is neither permitted nor denied by best guess record for domain of davem@davemloft.net) client-ip=2620:137:e000::1:9; Authentication-Results: mx.google.com; spf=neutral (google.com: 2620:137:e000::1:9 is neither permitted nor denied by best guess record for domain of davem@davemloft.net) smtp.mailfrom=davem@davemloft.net Received: from localhost (unknown [IPv6:2601:601:9f80:35cd::3d5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id ECD2F14C61512; Mon, 11 Mar 2019 11:14:13 -0700 (PDT) Date: Mon, 11 Mar 2019 11:14:13 -0700 (PDT) Message-Id: <20190311.111413.1140896328197448401.davem@davemloft.net> To: mst@redhat.com Cc: jasowang@redhat.com, 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() From: David Miller In-Reply-To: <20190311095405-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> X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=iso-2022-jp Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Mon, 11 Mar 2019 11:14:14 -0700 (PDT) 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: 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()"