From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anshuman Khandual Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Date: Wed, 25 Jul 2018 08:56:23 +0530 Message-ID: <4062dd48-2b5b-e454-e860-c6bfe321ebdc__49572.6302652203$1532489077$gmane$org@linux.vnet.ibm.com> References: <20180720035941.6844-1-khandual@linux.vnet.ibm.com> <20180720161541-mutt-send-email-mst@kernel.org> <8f51d2c6-cc0c-9e42-f0fd-a8a33acc8b83@linux.vnet.ibm.com> <20180723120511-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180723120511-mutt-send-email-mst@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: robh@kernel.org, srikar@linux.vnet.ibm.com, linuxram@us.ibm.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, hch@infradead.org, paulus@samba.org, joe@perches.com, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, haren@linux.vnet.ibm.com, david@gibson.dropbear.id.au List-Id: virtualization@lists.linuxfoundation.org On 07/23/2018 02:38 PM, Michael S. Tsirkin wrote: > On Mon, Jul 23, 2018 at 11:58:23AM +0530, Anshuman Khandual wrote: >> On 07/20/2018 06:46 PM, Michael S. Tsirkin wrote: >>> On Fri, Jul 20, 2018 at 09:29:37AM +0530, Anshuman Khandual wrote: >>>> This patch series is the follow up on the discussions we had before about >>>> the RFC titled [RFC,V2] virtio: Add platform specific DMA API translation >>>> for virito devices (https://patchwork.kernel.org/patch/10417371/). There >>>> were suggestions about doing away with two different paths of transactions >>>> with the host/QEMU, first being the direct GPA and the other being the DMA >>>> API based translations. >>>> >>>> First patch attempts to create a direct GPA mapping based DMA operations >>>> structure called 'virtio_direct_dma_ops' with exact same implementation >>>> of the direct GPA path which virtio core currently has but just wrapped in >>>> a DMA API format. Virtio core must use 'virtio_direct_dma_ops' instead of >>>> the arch default in absence of VIRTIO_F_IOMMU_PLATFORM flag to preserve the >>>> existing semantics. The second patch does exactly that inside the function >>>> virtio_finalize_features(). The third patch removes the default direct GPA >>>> path from virtio core forcing it to use DMA API callbacks for all devices. >>>> Now with that change, every device must have a DMA operations structure >>>> associated with it. The fourth patch adds an additional hook which gives >>>> the platform an opportunity to do yet another override if required. This >>>> platform hook can be used on POWER Ultravisor based protected guests to >>>> load up SWIOTLB DMA callbacks to do the required (as discussed previously >>>> in the above mentioned thread how host is allowed to access only parts of >>>> the guest GPA range) bounce buffering into the shared memory for all I/O >>>> scatter gather buffers to be consumed on the host side. >>>> >>>> Please go through these patches and review whether this approach broadly >>>> makes sense. I will appreciate suggestions, inputs, comments regarding >>>> the patches or the approach in general. Thank you. >>> I like how patches 1-3 look. Could you test performance >>> with/without to see whether the extra indirection through >>> use of DMA ops causes a measurable slow-down? >> >> I ran this simple DD command 10 times where /dev/vda is a virtio block >> device of 10GB size. >> >> dd if=/dev/zero of=/dev/vda bs=8M count=1024 oflag=direct >> >> With and without patches bandwidth which has a bit wide range does not >> look that different from each other. >> >> Without patches >> =============== >> >> ---------- 1 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.95557 s, 4.4 GB/s >> ---------- 2 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.05176 s, 4.2 GB/s >> ---------- 3 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.88314 s, 4.6 GB/s >> ---------- 4 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.84899 s, 4.6 GB/s >> ---------- 5 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 5.37184 s, 1.6 GB/s >> ---------- 6 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.9205 s, 4.5 GB/s >> ---------- 7 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 6.85166 s, 1.3 GB/s >> ---------- 8 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.74049 s, 4.9 GB/s >> ---------- 9 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 6.31699 s, 1.4 GB/s >> ---------- 10 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.47057 s, 3.5 GB/s >> >> >> With patches >> ============ >> >> ---------- 1 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.25993 s, 3.8 GB/s >> ---------- 2 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.82438 s, 4.7 GB/s >> ---------- 3 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.93856 s, 4.4 GB/s >> ---------- 4 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.83405 s, 4.7 GB/s >> ---------- 5 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 7.50199 s, 1.1 GB/s >> ---------- 6 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.28742 s, 3.8 GB/s >> ---------- 7 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 5.74958 s, 1.5 GB/s >> ---------- 8 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 1.99149 s, 4.3 GB/s >> ---------- 9 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 5.67647 s, 1.5 GB/s >> ---------- 10 --------- >> 1024+0 records in >> 1024+0 records out >> 8589934592 bytes (8.6 GB, 8.0 GiB) copied, 2.93957 s, 2.9 GB/s >> >> Does this look okay ? > > You want to test IOPS with lots of small writes and using > raw ramdisk on host. Hello Michael, I have conducted the following experiments and here are the results. TEST SETUP ========== A virtio block disk is mounted on the guest as follows.
In the host back end its an QEMU raw image on tmpfs file system. disk: -rw-r--r-- 1 libvirt-qemu kvm 5.0G Jul 24 06:26 disk2.img mount: size=21G on /mnt type tmpfs (rw,relatime,size=22020096k) TEST CONFIG =========== FIO (https://linux.die.net/man/1/fio) is being run with and without the patches. Read test config: [Sequential] direct=1 ioengine=libaio runtime=5m time_based filename=/dev/vda bs=4k numjobs=16 rw=read unlink=1 iodepth=256 Write test config: [Sequential] direct=1 ioengine=libaio runtime=5m time_based filename=/dev/vda bs=4k numjobs=16 rw=write unlink=1 iodepth=256 The virtio block device comes up as /dev/vda on the guest with /sys/block/vda/queue/nr_requests=128 TEST RESULTS ============ Without the patches ------------------- Read test: Run status group 0 (all jobs): READ: bw=550MiB/s (577MB/s), 33.2MiB/s-35.6MiB/s (34.9MB/s-37.4MB/s), io=161GiB (173GB), run=300001-300009msec Disk stats (read/write): vda: ios=42249926/0, merge=0/0, ticks=1499920/0, in_queue=35672384, util=100.00% Write test: Run status group 0 (all jobs): WRITE: bw=514MiB/s (539MB/s), 31.5MiB/s-34.6MiB/s (33.0MB/s-36.2MB/s), io=151GiB (162GB), run=300001-300009msec Disk stats (read/write): vda: ios=29/39459261, merge=0/0, ticks=0/1570580, in_queue=35745992, util=100.00% With the patches ---------------- Read test: Run status group 0 (all jobs): READ: bw=572MiB/s (600MB/s), 35.0MiB/s-37.2MiB/s (36.7MB/s-38.0MB/s), io=168GiB (180GB), run=300001-300006msec Disk stats (read/write): vda: ios=43917611/0, merge=0/0, ticks=1934268/0, in_queue=35531688, util=100.00% Write test: Run status group 0 (all jobs): WRITE: bw=546MiB/s (572MB/s), 33.7MiB/s-35.0MiB/s (35.3MB/s-36.7MB/s), io=160GiB (172GB), run=300001-300007msec Disk stats (read/write): vda: ios=14/41893878, merge=0/0, ticks=8/2107816, in_queue=35535716, util=100.00% Results with and without the patches are similar.