Hi Georg, I am using CentOS 5.7 and 5.8. Using ext3 FS on LVM. This issue happens without LVM, so LVM is not the cause, I think. I changed the I/O size at the application level to 16KB then, 16KB I/O and 4KB I/O are issued at scsi level as following. (SYSPREAD is application level I/O and SCSI is scsi i/o dispatching from systemtap.) ============================================= SYSPREAD random(8472) 3, 0x16fc5200, 16384, 128137183232 SCSI random(8472) 0 1 0 0 start-sector: 226321183 size: 4096 bufflen 4096 FROM_DEVICE 1354354008068009 SCSI random(8472) 0 1 0 0 start-sector: 226323431 size: 16384 bufflen 16384 FROM_DEVICE 1354354008075927 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 21807710208 SCSI random(8472) 0 1 0 0 start-sector: 1889888935 size: 4096 bufflen 4096 FROM_DEVICE 1354354008085128 SCSI random(8472) 0 1 0 0 start-sector: 1889891823 size: 16384 bufflen 16384 FROM_DEVICE 1354354008097161 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 139365318656 SCSI random(8472) 0 1 0 0 start-sector: 254092663 size: 4096 bufflen 4096 FROM_DEVICE 1354354008100633 SCSI random(8472) 0 1 0 0 start-sector: 254094879 size: 16384 bufflen 16384 FROM_DEVICE 1354354008111723 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 60304424960 SCSI random(8472) 0 1 0 0 start-sector: 58119807 size: 4096 bufflen 4096 FROM_DEVICE 1354354008120469 SCSI random(8472) 0 1 0 0 start-sector: 58125415 size: 16384 bufflen 16384 FROM_DEVICE 1354354008126343 ============================================ Do you have any idea what's going on ? On Sat, Dec 1, 2012 at 11:26 PM, Georg Schönberger <gschoenberger@xxxxxxxxxxxxxxxx> wrote: > ----- Original Message ----- >> From: "Hiroyuki Yamada" <mogwaing@xxxxxxxxx> >> To: fio@xxxxxxxxxxxxxxx >> Sent: Saturday, 1 December, 2012 9:31:42 AM >> Subject: I/O is issued twice at scsi level >> >> Hi, >> >> I am using fio for benchmarking random read IOPS of files. >> (Test configuration is listed at the bottom.) >> >> I have traced I/Os from fio by systemtap and >> noticed that the number of I/Os at scsi level is twice as many as the >> number of I/Os at vfs level. >> But, I/O size at both scsi level and vfs level shown as 4KB, so >> simply >> measured 1/2 performance. >> I also tried by benchmarking tools and the same issue happend. >> so, it's not fio specific issue. >> But, I am wondering if any of you knows the reason for that or some >> hints. >> >> >> Test configuration. >> ================= >> ioengine=psync >> rw=randread >> numjobs=1 >> blocksize=4096 >> filename=file_morethan_100G >> thread >> runtime=60 >> randrepeat=0 >> ================= >> (I clean up page caches every time before mesurement.) >> >> >> Thanks, >> Hiroyuki >> -- >> To unsubscribe from this list: send the line "unsubscribe fio" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > This is very interesting as I am currently investigating a 50% performance gap between two performance systems. > I am inspecting a 50% difference concerning 4k random read IOPS for the same device on different systems (a SCSI SSD), one Ubuntu 12.04 and one CentOS. > > Can you provide some more information about your platform? > > Thanks, Georg -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
