Bottom half in linux kernel
- 1. BinaryExe LLC https://exebinary.wordpress.com/ Bottom Half in Linux Kernel (LK)
- 2. BinaryExe LLC https://exebinary.wordpress.com/ Bottom half Execute in Interrupt context after interrupt handler (often called Top Half) complete
- 3. BinaryExe LLC https://exebinary.wordpress.com/ Why Bottom half Interrupt potentially other important code High priory interrupt stop execution of low priority Worst case of IRQ_DISABLED disable all interrupt Interrupt are often time critical Can’t be block as it is in interrupt context
- 4. BinaryExe LLC https://exebinary.wordpress.com/ Type of Bottom half in LK 2.6 Softirqs Tasklets Work queues
- 5. BinaryExe LLC https://exebinary.wordpress.com/ Softirq Created at compile time Of same/different type can run simultaneously on any processor For performance critical such networking Softirq doesn’t preempt other Softirq Tasklets and kernel timers built on top of Softirq
- 6. BinaryExe LLC https://exebinary.wordpress.com/ Softirq → Index (priority) → Description HI_SOFTIRQ 0 Handles high priority tasklets TIMER_SOFTIRQ 1 Tasklets related to timer interrupts NET_TX_SOFTIRQ 2 Transmits packets to network cards NET_RX_SOFTIRQ 3 Receives packets from network cards SCSI_SOFTIRQ 4 Post-interrupt processing of SCSI commands TASKLET_SOFTIRQ 5 Handles regular tasklets
- 7. BinaryExe LLC https://exebinary.wordpress.com/ Softirq Initialization open_softirq() Activation raise_softirq( ) Masking __local_bh_disable( )/__local_bh_enable( ) Execution void softirq_handler(struct softirq_action *)
- 8. BinaryExe LLC https://exebinary.wordpress.com/ Tasklet Built on top of Softirqs i.e. HI_SOFTIRQ and TASKLET_SOFTIRQ HI_SOFTIRQ Tasklet runs prior to TASKLET_SOFTIRQ
- 9. BinaryExe LLC https://exebinary.wordpress.com/ Tasklet Initialization tasklet_init( ) Activation tasklet_schedule( ) or asklet_hi_schedule( ) Masking tasklet_disable( )/tasklet_enable( ) Execution tasklet_action( )/tasklet_hi_action( )
- 10. BinaryExe LLC https://exebinary.wordpress.com/ Softirq <-----------> Tasklet Only for high frequency and highly threaded uses Created statically Simultaneous execution of same Softirq For all other cases where interrupt context is needed Can be created statically or dynamically Two of same Tasklet can’ get executed but two different Tasklet can run on different processor Built on top of Softirq
- 11. BinaryExe LLC https://exebinary.wordpress.com/ Work Queues Defers work in kernel thread also called worker thread Run in process context Used in case if deffered work can sleep
- 12. BinaryExe LLC https://exebinary.wordpress.com/ Workqueue implementation Initialization create_workqueue() - creates n worker threads (n - no of CPU) Activation queue_work( ) Masking
- 13. BinaryExe LLC https://exebinary.wordpress.com/ Tasklet/Softirq ←-- → Work queue Used when deferred work can’t sleep Not schedulable Used when deferred work can sleep Schedulable
- 14. BinaryExe LLC https://exebinary.wordpress.com/ Thanks If there is any question, send to [email protected]