What is a quiescent state in RCU?
Quiescent states for rcu are context switch, idle (either dynticks or the idle loop), and user-mode execution, while quiescent states for rcu_bh are any code outside of softirq with interrupts enabled. Note that an quiescent state for rcu is also a quiescent state for rcu_bh.
What does RCU stand for in Linux?
Abstract. Read–copy update (RCU) is a synchronization mechanism used heavily in key components of the Linux kernel, such as the virtual filesystem (VFS), to achieve scalability by exploiting RCU’s ability to allow concurrent reads and updates.
What is RCU fundamentally?
RCU is made up of three fundamental mechanisms, the first being used for insertion, the second being used for deletion, and the third being used to allow readers to tolerate concurrent insertions and deletions.
What is RCU callback?
The Read-Copy-Update (RCU) system is a lockless mechanism for mutual exclusion inside the kernel. As a consequence of performing RCU operations, call-backs are sometimes queued on CPUs to be performed at a future moment when removing memory is safe.
What is Rcu_read_lock?
rcu_read_lock() void rcu_read_lock(void); Used by a reader to inform the reclaimer that the reader is entering an RCU read-side critical section. It is illegal to block while in an RCU read-side critical section, though kernels built with CONFIG_PREEMPT_RCU can preempt RCU read-side critical sections.
What is soft IRQ?
SoftIrqs allow the critical part of servicing hardware interrupts to be as short as possible; instead of having to process the entire hw interrupt on the spot, the important data is read off the device into RAM or otherwise, and then a SoftIrq is started to finish the work.
What is Rcu_preempt?
The preempt parameter indicates if task blocked with help of schedule() or if it was a kernel path (such as return from interrupts or system calls) that called into the scheduler to preempt the currently running task.
What is Softirq and Tasklets?
Generally speaking, softirqs are re-entrant functions and must explicitly protect their data structures with spin locks. Tasklets differ from softirqs because a tasklet is always serialized with respect to itself; in other words, a tasklet cannot be executed by two CPUs at the same time.
What is the use of jiffies?
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.
What is Sysconf (_ Sc_clk_tck?
The number of clock ticks per second can be found by the sysconf system call, printf (“_SC_CLK_TCK = %ld\n”, sysconf (_SC_CLK_TCK)); A typical value of clock ticks per second is 100. That is, in this case, there is a clock tick every 10 milliseconds or 0.01 second.
What is Kworker task?
“kworker” is a placeholder process for kernel worker threads, which perform most of the actual processing for the kernel, especially in cases where there are interrupts, timers, I/O, etc. These typically correspond to the vast majority of any allocated “system” time to running processes.
What is softIRQ in Linux?
Can softIRQ be interrupted?
Softirqs run at a high priority (though with an interesting exception, described below), but with hardware interrupts enabled. They thus will normally preempt any work except the response to a “real” hardware interrupt.
What are jiffies RTOS?
What is Getconf in Linux?
The getconf command, invoked with the PathConfiguration and Pathname parameters, writes the value of the variable, as specified by the PathConfiguration parameter for the path specified by the PathName parameter, to standard output.
What are Linux Kworker processes?
What is a quiescent state?
The idea is to identify a quiescent state in each thread. A quiescent state is a bit like the opposite of a critical section. It’s some point in the thread’s execution that lies outside all related critical sections performed by that thread.
Are all quiescent-state configurations stable?
The stability of many quiescent-state configurations was studied, for fluid layers of infinite or very large extension, of pure-fluid/mixtures, with/without free surface. Nonetheless, many other configurations are not yet analyzed.
Where should the quiescent state be placed in Java?
Therefore, at a very minimum, the quiescent state should lie somewhere outside the broadcast function. Wherever we choose to put the quiescent state, we must notify the MemoryReclaimer object about it. In our case, we’ll require threads to call onQuiescentState.
When does the quiescent state lose its stability?
Intuitively, the quiescent state loses its stability when ∇ → ρ ( p, T, C) ⋅ ∇ → ψ exceeds a threshold value (positive, by the dissipative effects). This analysis supplies it, together with the data of the oscillatory motions emerging at onset from the rest-state instability.