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xen-devel
Re: [Xen-devel] question about disk performance in domU
So the "Timing buffered disk reads" show much higher results. I see the DMA
zone is larger in domU, but since this is mapped to a loopback file I'm guessing
the physical disk performance should only be affected by what dom0's DMA zone is
set to on the node running the domU if that is all that was going on. But dom0
performance seems comparable to native linux.
Is this huge "timing buffered disk read" difference accurate? Does the domU
benefit from some other cache of the loopback file in dom0? How does the DMA
setting in domU work?
Thanks for any insights,
Tim
On Mon, 21 Nov 2005 09:41:08 -0600
xuehai zhang <hai@xxxxxxxxxxxxxxx> wrote:
> Hi all,
>
> When I ran the experiments to compare an application's execution time in both
> a domU (named cctest1) and a native Linux machine (named ccn10), I noticed
> the application executes faster in domU. The host of the domU (named ccn9)
> and ccn10 are two nodes of a cluster and they have same hardware
> configurations. domU (cctest1) is created by exporting loopback files from
> dom0 on ccn9 as VBD backends. The application execution logs there might be
> some disk I/O difference between cctest and ccn10, so I did some disk
> performance profiling with "hdparms" on cctest1 (domU), ccn10 (native Linux),
> ccn9 (dom0), and ccn9 (native Linux). Also, I checked the "DMA" config
> information from the output of dmesg. I tried to run "hdparm -i" and "hdparm
> -I" but they didn't work. Seems they didn't work with SCSI disks. The
> following are the results. Thanks in advance for your help.
> Best,
> Xuehai
>
> 1. cctest1 (dumU)
> *****************************************************************************
> ********************* cctest1$ df -lh
> Filesystem Size Used Avail Use% Mounted on
> /dev/sda1 1.5G 1.1G 306M 78% /
> tmpfs 62M 4.0K 62M 1% /dev/shm
> /dev/sda6 4.2G 3.6G 453M 89% /tmp
> /dev/sda5 938M 205M 685M 23% /var
>
> cctest1$ dmesg | grep DMA
> DMA zone: 101376 pages, LIFO batch:16
>
> cctest1$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
>
> Timing cached reads: 512 MB in 2.00 seconds = 256.00 MB/sec
> Timing buffered disk reads: 44 MB in 3.00 seconds = 14.67 MB/sec
>
> Timing cached reads: 528 MB in 2.01 seconds = 262.69 MB/sec
> Timing buffered disk reads: 84 MB in 3.08 seconds = 27.27 MB/sec
>
> Timing cached reads: 520 MB in 2.00 seconds = 260.00 MB/sec
> Timing buffered disk reads: 120 MB in 3.06 seconds = 39.22 MB/sec
>
> Timing cached reads: 520 MB in 2.00 seconds = 260.00 MB/sec
> Timing buffered disk reads: 150 MB in 3.06 seconds = 49.02 MB/sec
>
> Timing cached reads: 536 MB in 2.00 seconds = 268.00 MB/sec
> Timing buffered disk reads: 178 MB in 3.17 seconds = 56.15 MB/sec
>
> Timing cached reads: 536 MB in 2.00 seconds = 268.00 MB/sec
> Timing buffered disk reads: 204 MB in 3.08 seconds = 66.23 MB/sec
>
> Timing cached reads: 532 MB in 2.00 seconds = 266.00 MB/sec
> Timing buffered disk reads: 228 MB in 3.13 seconds = 72.84 MB/sec
>
> Timing cached reads: 540 MB in 2.01 seconds = 268.66 MB/sec
> Timing buffered disk reads: 248 MB in 3.04 seconds = 81.58 MB/sec
>
> Timing cached reads: 540 MB in 2.00 seconds = 270.00 MB/sec
> Timing buffered disk reads: 266 MB in 3.06 seconds = 86.93 MB/sec
>
> Timing cached reads: 532 MB in 2.00 seconds = 266.00 MB/sec
> Timing buffered disk reads: 282 MB in 3.06 seconds = 92.16 MB/sec
>
> *****************************************************************************
> *********************
>
>
> 2. ccn10 (native Linux)
>
> *****************************************************************************
> *********************
>
> ccn10$ df -lh
> Filesystem Size Used Avail Use% Mounted on
> /dev/sda1 1.5G 1.3G 149M 90% /
> tmpfs 252M 0 252M 0% /dev/shm
> /dev/sda6 4.2G 3.6G 358M 92% /tmp
> /dev/sda5 938M 706M 184M 80% /var
>
> ccn10$ dmesg | grep DMA
> DMA zone: 4096 pages, LIFO batch:1
>
> ccn10$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
>
> Timing cached reads: 516 MB in 2.00 seconds = 257.78 MB/sec
> Timing buffered disk reads: 62 MB in 3.03 seconds = 20.47 MB/sec
>
> Timing cached reads: 524 MB in 2.01 seconds = 261.00 MB/sec
> Timing buffered disk reads: 62 MB in 3.01 seconds = 20.61 MB/sec
>
> Timing cached reads: 516 MB in 2.00 seconds = 257.65 MB/sec
> Timing buffered disk reads: 62 MB in 3.01 seconds = 20.61 MB/sec
>
> Timing cached reads: 524 MB in 2.00 seconds = 262.04 MB/sec
> Timing buffered disk reads: 62 MB in 3.01 seconds = 20.61 MB/sec
>
> Timing cached reads: 516 MB in 2.00 seconds = 257.78 MB/sec
> Timing buffered disk reads: 62 MB in 3.02 seconds = 20.51 MB/sec
>
> Timing cached reads: 524 MB in 2.00 seconds = 261.78 MB/sec
> Timing buffered disk reads: 62 MB in 3.02 seconds = 20.52 MB/sec
>
> Timing cached reads: 516 MB in 2.00 seconds = 257.78 MB/sec
> Timing buffered disk reads: 62 MB in 3.02 seconds = 20.51 MB/sec
>
> Timing cached reads: 524 MB in 2.00 seconds = 261.78 MB/sec
> Timing buffered disk reads: 62 MB in 3.02 seconds = 20.50 MB/sec
>
> Timing cached reads: 516 MB in 2.00 seconds = 257.40 MB/sec
> Timing buffered disk reads: 64 MB in 3.09 seconds = 20.73 MB/sec
>
> Timing cached reads: 524 MB in 2.01 seconds = 260.87 MB/sec
> Timing buffered disk reads: 62 MB in 3.01 seconds = 20.61 MB/sec
>
> *****************************************************************************
> *********************
>
>
> 3. ccn9 (dom0)
> *****************************************************************************
> *********************
>
> ccn9$ df -lh
> Filesystem Size Used Avail Use% Mounted on
> /dev/sda1 1.5G 1.1G 306M 78% /
> tmpfs 62M 4.0K 62M 1% /dev/shm
> /dev/sda6 4.2G 3.6G 453M 89% /tmp
> /dev/sda5 938M 205M 685M 23% /var
>
> ccn9$ dmesg | grep DMA
> DMA zone: 32768 pages, LIFO batch:8
>
> ccn9$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
>
> Timing cached reads: 504 MB in 2.00 seconds = 252.00 MB/sec
> Timing buffered disk reads: 60 MB in 3.14 seconds = 19.11 MB/sec
>
> Timing cached reads: 516 MB in 2.00 seconds = 258.00 MB/sec
> Timing buffered disk reads: 62 MB in 3.15 seconds = 19.68 MB/sec
>
> Timing cached reads: 512 MB in 2.00 seconds = 256.00 MB/sec
> Timing buffered disk reads: 60 MB in 3.08 seconds = 19.48 MB/sec
>
> Timing cached reads: 516 MB in 2.00 seconds = 258.00 MB/sec
> Timing buffered disk reads: 58 MB in 3.02 seconds = 19.21 MB/sec
>
> Timing cached reads: 516 MB in 2.01 seconds = 256.72 MB/sec
> Timing buffered disk reads: 60 MB in 3.12 seconds = 19.23 MB/sec
>
> Timing cached reads: 520 MB in 2.00 seconds = 260.00 MB/sec
> Timing buffered disk reads: 60 MB in 3.13 seconds = 19.17 MB/sec
>
> Timing cached reads: 520 MB in 2.01 seconds = 258.71 MB/sec
> Timing buffered disk reads: 60 MB in 3.13 seconds = 19.17 MB/sec
>
> Timing cached reads: 520 MB in 2.01 seconds = 258.71 MB/sec
> Timing buffered disk reads: 60 MB in 3.06 seconds = 19.61 MB/sec
>
> Timing cached reads: 516 MB in 2.01 seconds = 256.72 MB/sec
> Timing buffered disk reads: 60 MB in 3.14 seconds = 19.11 MB/sec
>
> Timing cached reads: 516 MB in 2.00 seconds = 258.00 MB/sec
> Timing buffered disk reads: 60 MB in 3.15 seconds = 19.05 MB/sec
>
> *****************************************************************************
> *********************
>
> 4. ccn9 (native Linux)
> *****************************************************************************
> ********************* ccn9$ df -lh
> Filesystem Size Used Avail Use% Mounted on
> /dev/sda1 1.5G 1.1G 306M 78% /
> tmpfs 62M 4.0K 62M 1% /dev/shm
> /dev/sda6 4.2G 3.6G 453M 89% /tmp
> /dev/sda5 938M 205M 685M 23% /var
>
> ccn9 $ dmesg | grep DMA
> DMA zone: 4096 pages, LIFO batch:1
>
> ccn9$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
> /dev/sda1:
> Timing cached reads: 492 MB in 2.01 seconds = 244.57 MB/sec
> Timing buffered disk reads: 62 MB in 3.10 seconds = 20.01 MB/sec
>
> Timing cached reads: 484 MB in 2.01 seconds = 241.07 MB/sec
> Timing buffered disk reads: 48 MB in 3.01 seconds = 15.95 MB/sec
>
> Timing cached reads: 484 MB in 2.00 seconds = 241.67 MB/sec
> Timing buffered disk reads: 62 MB in 3.03 seconds = 20.45 MB/sec
>
> Timing cached reads: 484 MB in 2.01 seconds = 241.31 MB/sec
> Timing buffered disk reads: 62 MB in 3.01 seconds = 20.57 MB/sec
>
> Timing cached reads: 480 MB in 2.01 seconds = 239.08 MB/sec
> Timing buffered disk reads: 62 MB in 3.03 seconds = 20.49 MB/sec
>
> Timing cached reads: 488 MB in 2.01 seconds = 243.31 MB/sec
> Timing buffered disk reads: 62 MB in 3.05 seconds = 20.31 MB/sec
>
> Timing cached reads: 484 MB in 2.01 seconds = 241.31 MB/sec
> Timing buffered disk reads: 62 MB in 3.01 seconds = 20.61 MB/sec
>
> Timing cached reads: 484 MB in 2.00 seconds = 241.67 MB/sec
> Timing buffered disk reads: 62 MB in 3.01 seconds = 20.59 MB/sec
>
> Timing cached reads: 488 MB in 2.01 seconds = 242.34 MB/sec
> Timing buffered disk reads: 62 MB in 3.01 seconds = 20.59 MB/sec
>
> Timing cached reads: 484 MB in 2.01 seconds = 240.35 MB/sec
> Timing buffered disk reads: 62 MB in 3.09 seconds = 20.09 MB/sec
> *****************************************************************************
> *********************
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
>
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