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in Linux kernel source code, I find below code:

    h++;
    pending >>= 1;

It is part of __do_softirq(void). But what does ">>=" mean? Why isn't it ">>" as I remember? Thanks!

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16

It simply does 

pending = pending >>1;

In short it divides by 2 an unsigned int.

That's the same construct than +=, /=, etc.

It's not just pending >>1 as you remember because that wouldn't store the result of the shift operation in the variable.

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It divides by 2 an unsigned int. C does not specify what happens to a signed int. You're better off using /= in that case.
yes. precision added. I don't think this construct for dividing by two is really useful today as all compilers probably optimize the /=2 on unsigned int. You should probably use it mainly when you use the int to store bits.
@DougCurrie you mean for a negative signed integer.
Thank you for detailed explaination of the "="! I leanrt it.
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It's equivalent to

pending = pending >> 1;

Which bitshifts right the bits in pending. This would have the effect of dividing an unsigned int by 2. >> and << are the bitshift operators, and the combination with = behaves the same way += and /= do.

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