And where is the corresponding updated atime write? Buffered? Regards, Andrey On Mon, Dec 3, 2012 at 5:43 PM, Jens Axboe <axboe@xxxxxxxxx> wrote: > Quick guess - it's updating the mtime/atime on the inode? > > > On 2012-12-02 10:23, Hiroyuki Yamada wrote: >> I figured out what is going on, but I don't know what it is for. >> >> Ext3 filesystem has some 4KB data in each 4096KB(8192 sectors) data. >> Visually, data is aligned like the following. >> >> |4KB|4096KB|4KB|4096KB|4KB|4096KB| ... >> >> And 4096KB area in only accessible by application programs. >> When accessing the first 4096KB area for the first time, >> then OS reads the 4KB just before the 4096KB area first >> and then read the requested data in the 4096KB area. >> >> When accessing a large file (compared to the DRAM size) randomly, >> every I/O has rare chance of hitting page cahce, >> so every I/O request comes together with 4KB I/O. >> >> The thing is what the 4KB data is for ? >> Is this location metadata for filesystem ? >> Is there any way I can remove this ? >> Or Is there any way I can clear the 4096KB area only ? >> >> Any comments and advices are appreciated. >> >> (I tested in many machines with many kernel versions. this happens in >> all machines.) >> >> Thanks. >> >> On Sat, Dec 1, 2012 at 11:51 PM, Hiroyuki Yamada <mogwaing@xxxxxxxxx> wrote: >>> 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 >> > > > -- > Jens Axboe > > -- > 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 -- 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
