Category Archives: develope

From scala Array[String] / Seq[String] to java varargs

While testing performance of redis these days, I need to use mset() interface of jedis (a java version redis client). But the prototype of mset() in jedis is:

Firstly I write my scala code like:

But it report compiling errors:

After searching many documents about scala/java on… Read more »

Performance test for unikernels (Rumpkernel and OSv)

Unikernels are specialised, single-address-space machine images constructed by using library operating systems. The concept of Unikernel is very old (Since 1980s in embeded system), but become more and more popular in this cloud computing age for its portability and security. In recent days, I tested two famous unikernel production: Rumpkernel… Read more »

How to disable the creation of the rescue initramfs on CentOS 7

I was trying to install new linux kernel (4.4-rc5) in my CentOS 7 server. But when I run “sudo make install” it report

The initramfs-0-rescue-XXX file occupied too much space in boot device. Then I found this article. But after adding dracut_rescue_image=”no” into /etc/dracut.conf, the problem was still exist…. Read more »

“kmem_cache_create: duplicate cache XXX”

In my kernel module, firstly I wrote:

In centos 7, this module works fine, but after port to centos 6, this kernel module reports:

The key to this problme is in the implementation of kmem_cache_create() in 2.6.32 linux kernel (for centos 6):

After creating a new pool,… Read more »

Use recv() instead of read() for socket

When we use read() to read data from a socket like:

the read() may return ‘ret’ which is small than sizeof(struct msg) even the socket is not O_NONBLOCKING. The correct way is:

Then, recv() will wait util all sizeof(struct msg) be read out.

A example of Mesos Python Framework to calculate Pi

I have written an example of Mesos Framework by python. It simply calculate “Pi” by using Mento-Carlo algorithm The whole source code is at https://github.com/RobinDong/mesos-python-examples/tree/master/calculate_pi At beginning, I use python threading in “launchTask()”:

But I found out that the executors only spend a small part of CPU resource in… Read more »

Override the __init__ of BaseHTTPRequestHandler in python

Currently, I am writing some python program for the front of our storage system. By using ‘BaseHTTPRequestHandler’ and ‘ThreadedHTTPServer’, we could implement a simple multi-thread http server quickly. But after add ‘__init__()’ for our ‘MyHandler’, it doesn’t work correctly now:

Then I found this statement in python docs:

Read more »

128bit atomic operation in arm64

In x86_64 architecture, we could use cmpxchg16b to compare and exchange a 128bit value in one atomic operation. But how to operate a 128bit value in aarch64 architecture (arm64) machine ? The answer is __atomic_compare_exchange(). As below code:

use “gcc test.c -o test” to compile code, but it reports:… Read more »