Link to this post 05 Aug 11

No, This is incrementing or decrementing the softirq count. The preempt_count is divided as follows.

For softirq count there are 8 bits(from 8 - 15) in preempt_count variable. So, the variable can be incremented upto 255.
This count says number of levels the softirqs are disabled(number of tymes local_bh_disable() is called) . decremented using local_bh_enable(). See the following code in softirq.c and preempt.h

# define add_preempt_count(val) do { preempt_count() += (val); } while (0)

static inline void __local_bh_disable(unsigned long ip, unsigned int cnt)

Here, count is 0x100.


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