01 Jan 2017
As DHH talks in his blog, writing software is hard, which I can’t agree
First of all, I declaim that I am at my 28.
Obviously it is not the age of a senior software engineer.
but I am one of the people who uses software very early, i.e. at 10 in 1999.
Coding is hard
The most thing I want to talk about is coding. DHH makes it clear that no
super-duper easiness will help you about coding. Problems get solved by using
new coding technique such as new languages, frameworks or libs, but not all.
Coding is still hard. Writing good code is not simply applying cool technique or
some super cool “best practices”.
If the code doesn’t solve the users’ problems, it means nothing.
If the code causes more problems after merged, it means nothing.
If the code breaks the system it belongs to, it means nothing.
You really want to make a good piece of coding. You learn many different things,
compute science theories, algorithms, language rules, different libraries, other programmers’ code and many
others. But it won’t make you great if your code breaks things.
Coding is something about the language
Even if you make hard to learn many techniques and apply them into your code, it
won’t get you right. So there is something between your code and good code.
Let’s think a bit further. You write your code in computer languages, and you
think it is the language used for you and computers only. But you are WRONG.
In fact, coding is not just coding for the computer. The final target you write to and compute with is not the computer, but the human being. I am not talking about the customers, but the involvees, including you and your team.
Maybe you are confused about this. Let me make it simpler. When you begin to write the code and get it shipped to customers, your team designs the product, writes the code, reviews and verify it before deliver.
And your customers use your product and feed back about it. You all get involved. Ideas and thoughts are communicated via the software, or simpler, the code.
The Final Goal
So that’s what the computer stands for, an invention to compute the human being.
PS: Happy New Year!
21 Aug 2016
Linux Kernel provides null_blk module since 3.13, which can be used for
benchmarking various block-layer implementations. Also it can be used as a
dummy device to diagnostic storage system issues.
Check your kernel has null_blk module
grep CONFIG_BLK_DEV_NULL /boot/config-$(uname -r)
grep CONFIG_BLK_DEV_NULL /proc/config
for example centos 7 has:
Use Null blk
the usage is much like zram,
just insmod this module:
you can find two 250 GB-sized block device added
nullb0 251:0 0 250G 0 disk
nullb1 251:1 0 250G 0 disk
and run some benchmark on them:
dd if=/dev/zero of=/dev/nullb0 bs=4k oflag=direct
dd if=/dev/nullb0 of=/dev/null bs=4k iflag=direct
hdparm -tT /dev/nullb0
aio-stress -O -s 64m -r 256k -i 1024 -b 1024 /dev/nullb0
fio --ioengine=libaio --readwrite=randread --bs=4k --filename /dev/nullb0 --name journal_test --thread --norandommap --numjobs=200 --iodepth=64 --runtime=30 --time_based --group_reporting
fio --ioengine=libaio --readwrite=randwrite --bs=4k --filename /dev/nullb0 --name journal_test --thread --norandommap --numjobs=200 --iodepth=64 --runtime=30 --time_based --group_reporting
if you turn on scsi_mq, you will find incredible iops on your fio
benchmarks, such as 5M iops on randread on my machine.
null_blk module has many parameters provided, use can tune:
submit_queues: the number of submission queues
gb: size in GiB
bs: block size in bytes
nr_devices: number of devices to register
completion_nsec: time in ns to complete a request in hardware
hw_queue_depth: queue depth for each hardware queue
for the case for debian backported 4.6.0 kernel:
sudo modinfo null_blk
author: Jens Axboe <email@example.com>
vermagic: 4.6.0-0.bpo.1-amd64 SMP mod_unload modversions
parm: submit_queues:Number of submission queues (int)
parm: home_node:Home node for the device (int)
parm: queue_mode:Block interface to use (0=bio,1=rq,2=multiqueue)
parm: gb:Size in GB (int)
parm: bs:Block size (in bytes) (int)
parm: nr_devices:Number of devices to register (int)
parm: use_lightnvm:Register as a LightNVM device (bool)
parm: irqmode:IRQ completion handler. 0-none, 1-softirq, 2-timer
parm: completion_nsec:Time in ns to complete a request in hardware. Default: 10,000ns (ulong)
parm: hw_queue_depth:Queue depth for each hardware queue. Default: 64
parm: use_per_node_hctx:Use per-node allocation for hardware context queues. Default: false (bool)
there parameters are also described in null blk kernel documentation
11 Apr 2015
Atomic operations are quite useful in concurrent programming, notably in the
implementations of lock-free algorithms. Many times when the locking algorithms
goes to the performance bottleneck, atomic operations come to save.
- NotAtomic (regular load and store)
- Unordered (to match java safe language memory model)
- Monotinic (or
- Acquire (or
- Release (or
- AcuireRelease (or
- SquentiallyConsistent (or
all atomic loads generate a
MOV and SquentiallyConsistent stores generate an
XCHG, other stores generate a
on ARM (before v8) and MIPS
Acquire, Release and SquentiallyConsistent requires barrier instructions for
every such operation. Loads and stores generate normal instructions.
Language Standard and Compiler, library implementations
- The new C++11
atomic header and C11
volatile variables (match SquentiallyConsistent)
__sync_* builtins (match SquentiallyConsistent)
if you want to use atomic operations before sticking to the new standards, there
are compiler builtins functions and libraries availabe to call proper asm
instructions to do these atomic operations.
gcc atomic operations Built-in Functions:
A Small Benchmark
I wrote a small program to benchmark the performance of atomic operations
against mutexes and spinlocks. It is hosted at GitHub.. You can clone the
repository and execute
make. It requires a modern c++ compiler with c++11
this sample output is on my 4-cores 2013-late Macbook Pro:
jobs: 1 total time: 614932094 ns average time: 6149 ns (Mutex)
jobs: 1 total time: 5132226 ns average time: 51 ns (SpinLock)
jobs: 1 total time: 4172785 ns average time: 41 ns (Atomic)
jobs: 2 total time: 746401303 ns average time: 7464 ns (Mutex)
jobs: 2 total time: 15983439 ns average time: 159 ns (SpinLock)
jobs: 2 total time: 9356120 ns average time: 93 ns (Atomic)
jobs: 4 total time: 42609222 ns average time: 426 ns (SpinLock)
jobs: 4 total time: 13734551 ns average time: 137 ns (Atomic)
jobs: 8 total time: 107958834 ns average time: 1079 ns (SpinLock)
jobs: 8 total time: 30681228 ns average time: 306 ns (Atomic)
jobs: 16 total time: 213277915 ns average time: 2132 ns (SpinLock)
jobs: 16 total time: 52189737 ns average time: 521 ns (Atomic)
29 Sep 2014
C++ 11 is taking place in chromium.
In short, the below c++11 features allowed currently:
- variadic templates
or « in template arguments
- stdint.h and inttypes
- variadic macros
Visit chromium-cpp page for more.
Similar effort is made by mozilla
14 Sep 2014
In my previous post ,
I listed the C++11 and C++14 status of some common compilers. Here I am coming
to do a more practical and complete study on C++11 (and C++14 if possible).
Okay, Let’s begin
Notably, GCC C++, Clang C++, IBM C++, and Microsoft C++ already implement most
or all C++11 features:
In additions, their belonging library:
- libstdc++ status
- libc++ status page is removed for the support is completed
There are two parts making a complete C++11 support, namely compiler support and library one.
A detailed table for similar purpose inf different C++11 Features of c++ compiler is made
at wiki.appache.org last updated at 2013,
or visit cpprocks one
C++11 STL Support
Projects in C++11
- CAF https://github.com/actor-framework
- boost https://github.com/boostorg/boost
Projects coworks under both of C++03 and C++11
- boost https://github.com/boostorg/boost
- intel tbb
C++14 and its succeeder, C++17
A detailed table for similar purpose inf different C++14 Features of c++ compiler is made
or visit italiancpp.org one,
or visit cpprocks one
Although clang 3.4 has c++14 features complete, some c++14 users claims that
clang 3.4 has full support for C++14, it has several C++14-related bugs that
are fixed in 3.5.
clang has named experimental c++17 support to c++1z,
and gcc follows
- ISO Roadmap https://isocpp.org/std/status
Some words on c++11
you might wanna use
-std=c++11 instead of
-std=c++0x for a real C++11
support (gcc 4.8+, clang 3.3+ and etc)
you might wanna use
-std=c++14 instead of
-std=c++1y for a real C++14
support (gcc 5.0+, clang 3.5+ and etc)
For a complete c++11-feature support, please use:
- gcc 4.8.1 or later, (for regex library please use gcc 4.9)
- clang 3.3 or later
- MSVC 2014 CTP1+ or latest
- Inter C++ 15.0 or later