Hi Devendra, On Tue, Jan 31, 2012 at 1:28 AM, devendra rawat <devendra.rawat.singh@gmail.com> wrote:
Hi,
What are the Differences between CPU Hard-lockup and Soft-lockup.
When the watchdog is enabled, there is a HW timer that counts down. If the HW timer reaches 0, then it asserts (triggers an NMI or processor RESET). Normally, the watchdog has something like a 30 second timeout, and there is a watchdog thread which runs with a low real-time priority. So that places it at a higher priority than all of the normal threads. The watchdog normally kicks (resets) the timer once per second. When the timer reaches zero, then the hardlockup has considered to occur. On some architectures, this will cause an NMI (non-maskable interrupt) to fire. On architectures which don't support NMI, a reset will occur (in the reset case you get no reporting of hard lockup - the processor just reboots). If the watchdog timer interrupt is running, but the watchdog thread is not running for some period of time, then this is considered a soft lockup. Because the watchdog timer interrupt is running, we know that interrupts are enabled. The fact that the watchdog thread is not running means either that context switching has been disabled, or some interrupt or higher priority real-time thread is consuming 100% of the CPU. One common reason for hard-lockup is to disable interrupts and not reenable them. One common reason for soft lockup is when interrupts fire continuously (typically happens when writing a new drive and you forgot to deal with a particular interrupt source). -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com