On Tue, Sep 13, 2011 at 6:14 PM, Stefan Hajnoczi <stefa...@gmail.com> wrote: > On Tue, Sep 13, 2011 at 10:25 AM, Zhi Yong Wu <zwu.ker...@gmail.com> wrote: >> On Tue, Sep 13, 2011 at 3:14 PM, Stefan Hajnoczi >> <stefa...@linux.vnet.ibm.com> wrote: >>> On Tue, Sep 13, 2011 at 10:52:44AM +0800, Zhi Yong Wu wrote: >>>> This is real log when fio issued with bs=128K and bps=1000000(block >>>> I/O throttling): >>> >>> I would use 1024 * 1024 instead of 1000000 as the throughput limit. >>> 10^5 is not a multiple of 512 bytes and is not a nice value in KB/s >>> (976.5625). >> OK. next time, i will adopt this. >>> >>>> >>>> 8,2 0 1 0.000000000 24332 A WS 79958528 + 256 <- >>>> (253,2) 71830016 >>> >>> 256 blocks = 256 * 512 bytes = 128 KB per request. We know the maximum >>> request size from Linux is 128 KB so this makes sense. >>> >>>> Throughput (R/W): 0KiB/s / 482KiB/s >>> >>> What throughput do you get without I/O throttling? Either I/O >>> throttling is limiting too aggressively here or the physical disk is the >>> bottleneck (I double that since the write throughput value is very low). >>> We need to compare against the throughput when throttling is not >>> enabled. >> Without block I/O throttling. > [...] >> test: (g=0): rw=write, bs=128K-128K/128K-128K, ioengine=libaio, iodepth=1 >> Starting 1 process >> Jobs: 1 (f=1): [W] [100.0% done] [0K/13M /s] [0/103 iops] [eta 00m:00s] >> test: (groupid=0, jobs=1): err= 0: pid=2734 >> write: io=51,200KB, bw=12,933KB/s, iops=101, runt= 3959msec > > This shows that the physical disk is capable of far exceeding 1 MB/s > when I/O is not limited. So the earlier result where the guest only > gets 482 KiB/s under 1000000 bps limit shows that I/O limits are being > too aggressive. For some reason the algorithm is causing the guest to > get lower throughput than expected. > > It would be interesting to try with bps=$((10 * 1024 * 1024)). I > wonder if the algorithm has a constant overhead of a couple hundred > KB/s or if it changes with the much larger bps value. OK, i will try it tomorrow.
By the way, I/O throttling can be enabled now from libvirt guest's xml file when guest is started up. I have pushed its code changes to my git tree. git branch: ssh://wu...@repo.or.cz/srv/git/libvirt/zwu.git dev > > Stefan > -- Regards, Zhi Yong Wu
