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IDProjectCategoryView StatusLast Update
0016580CentOS-7kernelpublic2019-10-21 00:42
Reporterwuzeyi 
PriorityhighSeveritytweakReproducibilityalways
Status newResolutionopen 
Platformarm64OSCentOS Linux release (AltArch)OS Version4.14.0-115.el7a
Product Version7.6.1810 
Target VersionFixed in Version 
Summary0016580: Default maximum number of kilobytes to read-ahead for filesystems is too small
DescriptionI run Terasort on spark. Disk read performance is very low.
I Modify to change the /sys/block/sdd/queue/read_ahead_kb from 128(default) to 4096, and doubled the performance.

[root@localhost ~]# uname -r
4.14.0-115.el7a.0.1.aarch64
[root@localhost ~]# cat /etc/redhat-release
CentOS Linux release 7.6.1810 (AltArch)
[root@localhost ~]# cat /sys/block/sdd/queue/read_ahead_kb
128

I find that the default read_ahead_kb in redhat7.6 is 4096.

[root@localhost ~]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 7.6 (Maipo)
[root@localhost ~]# uname -r
4.14.0-115.el7a.aarch64
[root@localhost ~]# cat /sys/block/sdd/queue/read_ahead_kb
4096

The disk on RedHat is the same as CentOS.
This problem make the disk read performance on CentOS lower than RadHat.
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Issue History

Date Modified Username Field Change
2019-10-12 08:40 wuzeyi New Issue