Re: [Xen-devel] question about disk performance in domU - Tim Freeman - com.xensource.lists.xen-devel

6 messages in com.xensource.lists.xen-develRe: [Xen-devel] question about disk p...

From	Sent On	Attachments
xuehai zhang	21 Nov 2005 07:40
Tim Freeman	21 Nov 2005 12:44
Santos, Jose Renato G	21 Nov 2005 14:26
xuehai zhang	21 Nov 2005 14:41
Adam Heath	21 Nov 2005 14:50
xuehai zhang	21 Nov 2005 15:57

Subject:	Re: [Xen-devel] question about disk performance in domU
From:	Tim Freeman (tfre...@mcs.anl.gov)
Date:	11/21/2005 12:44:44 PM
List:	com.xensource.lists.xen-devel

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 <ha...@cs.uchicago.edu> 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 ***************************************************************************** *********************