What is Jiffies in Linux kernel?
What is Jiffies in Linux kernel?
The global variable “jiffies” holds the number of ticks that have occurred since the system booted. On boot, the kernel initializes the variable to zero, and it is incremented by one during each timer interrupt. Thus, because there are HZ timer interrupts in a second, there are HZ jiffies in a second.
How do you calculate Jiffies?
The size of a jiffy is determined by the value of the kernel constant HZ. The value of HZ varies across kernel versions and hardware platforms. On i386 the situation is as follows: on kernels up to and including 2.4. x, HZ was 100, giving a jiffy value of 0.01 seconds; starting with 2.6.
What is HZ Linux?
A jiffy is a kernel unit of time declared in . To understand jiffies, we need to introduce a new constant, HZ, which is the number of times jiffies is incremented in one second. Each increment is called a tick. In other words, HZ represents the size of a jiffy.
How long is a jiffy kernel?
In operating systems, especially Unix, a jiffy is the time between two successive clock ticks. Historically, this has been 10ms.
What is the use of Jiffies?
Uses. In electronics, a jiffy is the period of an alternating current power cycle, 1/60 or 1/50 of a second in most mains power supplies. In computing, a jiffy was originally the time between two ticks of the system timer interrupt.
How do you read uptime proc?
The first number is the total number of seconds the system has been up. The second number is how much of that time the machine has spent idle, in seconds.
How long is a jiffy in Linux?
Jiffy values for various Linux versions and platforms have typically varied between about 1 ms and 10 ms, with 10 ms reported as an increasingly common standard in the Jargon File.
What is Hz value in Linux kernel?
13, the HZ value is a kernel configuration parameter and can be 100, 250 (the default) or 1000, yielding a jiffies value of, respectively, 0.01, 0.004, or 0.001 seconds. Since kernel 2.6. 20, a further frequency is available: 300, a number that divides evenly for the common video frame rates (PAL, 25 HZ; NTSC, 30 HZ).
What is HZ value in Linux kernel?
Is HZ a tick rate?
Tick rate is the frequency at which a server updates game data, which is measured in hertz (Hz). For example, Battlefield 4 has servers with frequency rates of 20, 40, 60, or more hertz. If such servers were in Counter-Strike: Global Offensive, then we would say that they have a 20, 40, and 60 tick rate, respectively.
How many Jiffies are in a second?
Conversion number between second [s] and jiffy [j] is 60.
Is jiffy a real measurement of time?
FACT: a “jiffy” is an actual measurement of time. In physics (of the astro- and quantum variety) a jiffy is specifically defined as the time it takes light to travel 1 centimeter. That would be 0.000,000,000,033,300 seconds. Jiffy has also been bandied about as another term to describe the Planck interval.
How to convert jiffies to milli seconds in Linux?
If you tried to use HZ/200on a 10ms tick system, the integer division gives you 0 jiffies! So the rule of thumb is, be very careful using HZ for tiny values (those approaching 1 jiffie). To convert the other way, you would use: jiffies / HZ /* jiffies to seconds */ jiffies * 1000 / HZ /* jiffies to milliseconds */
How to specify a jiffiescount for a function?
The standard way of specifying a jiffiescount for a function is using HZ, like this: schedule_timeout(HZ / 10); /* Timeout after 1/10 second */ In most simple cases, this works fine.
How many jiffies are in a 10ms tick?
You may get a delay anywhere between 0.0001 and 1.999 timer ticks (0-2 ms, essentially). If you tried to use HZ/200on a 10ms tick system, the integer division gives you 0 jiffies! So the rule of thumb is, be very careful using HZ for tiny values (those approaching 1 jiffie).
