Speed of execution in term of code in some cases

-

Is “else if” faster than “switch() case”?


For small loops not required,For very big loop hash table is used for  switch case so faster execution.
But with good compiler with optimization enabled, it's same.


Why i++ is faster than i=i+1 in c


older compilers used 
(1)ADD      \\i+1
(2)Assignment operation          \i=x
for i=i+1

for i++
(1)INR

but currently good compilers with optimizations enabled creates same assembly code.


Comments

Post a Comment

Popular posts from this blog

Airtel Digital tv remote factory reset and reprogram

-
Following is the way to reset Airtel Digial tv universal remote reset procedure. 1. Press red button and ok button together untill red light blinks twice. 2. Release the buttons and press 980 buttons one by one (not together)   3. Red light will blink again two times, now press ok button. Reprogramming There are 5 basic functions which your new Airtel remote needs to learn about your TV 1. TV Power code 2. TV Mute code 3. AV code 4. TV VOL + code 5. TV VOL – code Steps for Universal remote setup: Step 1:  Bring Airtel digital TV remote in learning mode. Press and hold ‘’OK + Numeric 2” key for 3 seconds. The LED blinks twice to indicate that your Airtel remote is ready to learn. Step 2 :  Hold the source remote and Airtel remote in front of each other ( 3cm-6m apart). Step 3:  Press & release the key (First on Airtel remote and then on Source remote) which needs to be programmed in Airtel remote. Example: Press and release the TV Power key on both remotes and release. The A
Read more

Tracking Linux kworker threads

-
How to find out which part of kernel/module has created this workqueue. How to track a kworker-thread named for example ''kworker/0:3 to its origin in kernel-space? I found  this thread on lkml  that answers your question a little. (It seems even Linus himself was puzzled as to how to find out the origin of those threads.) Basically, there are two ways of doing this: $ echo workqueue:workqueue_queue_work > /sys/kernel/debug/tracing/set_event $ cat /sys/kernel/debug/tracing/trace_pipe > out.txt (wait a few secs) For this you will need  ftrace  to be compiled in your kernel, and to enable it with: mount -t debugfs nodev /sys/kernel/debug More information on the function tracer facilities of Linux is available in the  ftrace.txt documentation . This will output what threads are all doing, and is useful for tracing multiple small jobs. cat /proc/THE_OFFENDING_KWORKER/stack This will output the stack of a single thread doing a lot of work. It may allow you
Read more

Copy_to_user or copy_from_user instead of memcpy

-
Quite the contrary, it does handle the case for swapped out memory. Lets take a look at it, shall we? copy_to/from_user boils down to __copy_user in arch/i386/lib/usercopy.c: #define __copy_user(to,from,size) \ do { \ int __d0, __d1, __d2; \ __asm__ __volatile__( \ " cmp $7,%0\n" \ " jbe 1f\n" \ " movl %1,%0\n" \ " negl %0\n" \ " andl $7,%0\n" \ " subl %0,%3\n" \ "4: rep; movsb\n" \ " movl %3,%0\n"
Read more