hi all and thx Rik, I can't understand exactly how cpu gets "stuck"... I am wondering about what happens after the "hlt" instruction being executed, do all registers still keep their values ? does program counter stopped too ? or the power was shut just like I turn it off ? is there anything running stealthily ? the other question is, what is __builtin_constant_p() called by test_bit()? I can't even find it in the kernel codes. here are the test_bit macro: #define test_bit(nr,addr) \ (__builtin_constant_p(nr) ? \ constant_test_bit((nr),(addr)) : \ variable_test_bit((nr),(addr))) thx a lot ~~ ----- Original Message ----- From: "Rik van Riel" <riel@xxxxxxxxxxx> To: "P.F. Tsai" <yeltek@xxxxxxxxx> Cc: <kernelnewbies@xxxxxxxxxxxx> Sent: Thursday, April 21, 2005 11:06 AM Subject: Re: How does cpu_idle() work? > On Tue, 19 Apr 2005, P.F. Tsai wrote: > > > 1, how does need_resched() work? I dont understand how the test_bit() > > called inside is doing > > The bit can get set from interrupt context. All test_bit() does > is test if the bit is set. > > > 2, how does default_idle work? what does it do? what does halt mean? > > Halt basically tells the CPU to do nothing until something happens, > eg. an interrupt. This makes the CPU consume less power, yields the > hyperthread's resources to the other thread, etc... > > > 3, if once the cpu goes into idle with the while(1)-loop, will it be very > > busy (100% cpu utility) with looping around ?? > > Kind-of - if the cpu supports halt, it'll actually get "stuck" > in that instruction until an interrupt happens. > > > thx for helping.... > > Success with your homework ;) > > -- > "Debugging is twice as hard as writing the code in the first place. > Therefore, if you write the code as cleverly as possible, you are, > by definition, not smart enough to debug it." - Brian W. Kernighan -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
