On Mon, Mar 25, 2019 at 08:52:32PM +0200, Maxim Levitsky wrote: > Hi > > This is first round of benchmarks. > > The system is Intel(R) Xeon(R) Gold 6128 CPU @ 3.40GHz > > The system has 2 numa nodes, but only cpus and memory from node 0 were used to > avoid noise from numa. > > The SSD is Intel® Optane™ SSD 900P Series, 280 GB version > > > https://ark.intel.com/content/www/us/en/ark/products/123628/intel-optane-ssd-900p-series-280gb-1-2-height-pcie-x4-20nm-3d-xpoint.html > > > ** Latency benchmark with no interrupts at all ** > > spdk was complited with fio plugin in the host and in the guest. > spdk was first run in the host > then vm was started with one of spdk,pci passthrough, mdev and inside the > vm spdk was run with fio plugin. > > spdk was taken from my branch on gitlab, and fio was complied from source for > 3.4 branch as needed by the spdk fio plugin. > > The following spdk command line was used: > > $WORK/fio/fio \ > --name=job --runtime=40 --ramp_time=0 --time_based \ > --filename="trtype=PCIe traddr=$DEVICE_FOR_FIO ns=1" --ioengine=spdk \ > --direct=1 --rw=randread --bs=4K --cpus_allowed=0 \ > --iodepth=1 --thread > > The average values for slat (submission latency), clat (completion latency) and > its sum (slat+clat) were noted. > > The results: > > spdk fio host: > 573 Mib/s - slat 112.00ns, clat 6.400us, lat 6.52ms > 573 Mib/s - slat 111.50ns, clat 6.406us, lat 6.52ms > > > pci passthough host/ > spdk fio guest > 571 Mib/s - slat 124.56ns, clat 6.422us lat 6.55ms > 571 Mib/s - slat 122.86ns, clat 6.410us lat 6.53ms > 570 Mib/s - slat 124.95ns, clat 6.425us lat 6.55ms > > spdk host/ > spdk fio guest: > 535 Mib/s - slat 125.00ns, clat 6.895us lat 7.02ms > 534 Mib/s - slat 125.36ns, clat 6.896us lat 7.02ms > 534 Mib/s - slat 125.82ns, clat 6.892us lat 7.02ms > > mdev host/ > spdk fio guest: > 534 Mib/s - slat 128.04ns, clat 6.902us lat 7.03ms > 535 Mib/s - slat 126.97ns, clat 6.900us lat 7.03ms > 535 Mib/s - slat 127.00ns, clat 6.898us lat 7.03ms > > > As you see, native latency is 6.52ms, pci passthrough barely adds any latency, > while both mdev/spdk added about (7.03/2 - 6.52) - 0.51ms/0.50ms of latency. Milliseconds is surprising. The SSD's spec says 10us read/write latency. Did you mean microseconds? > > In addtion to that I added few 'rdtsc' into my mdev driver to strategically > capture the cycle count it takes it to do 3 things: > > 1. translate a just received command (till it is copied to the hardware > submission queue) > > 2. receive a completion (divided by the number of completion received in one > round of polling) > > 3. deliver an interupt to the guest (call to eventfd_signal) > > This is not the whole latency as there is also a latency between the point the > submission entry is written and till it is visible on the polling cpu, plus > latency till polling cpu gets to the code which reads the submission entry, > and of course latency of interrupt delivery, but the above measurements mostly > capture the latency I can control. > > The results are: > > commands translated : avg cycles: 459.844 avg time(usec): 0.135 > commands completed : avg cycles: 354.61 avg time(usec): 0.104 > interrupts sent : avg cycles: 590.227 avg time(usec): 0.174 > > avg time total: 0.413 usec > > All measurmenets done in the host kernel. the time calculated using tsc_khz > kernel variable. > > The biggest take from this is that both spdk and my driver are very fast and > overhead is just a thousand of cpu cycles give it or take. Nice! Stefan
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