Re: spin_lock_irqsave or spin_lock in work queue handlers?

["Peter Teoh" <htmldeveloper@xxxxxxxxx>]

I just found more information.   There is a whole movement of
converting semaphore to mutex in the kernel.   One active contributor
is "Daniel Walker", search for patch like "printer port driver:
semaphore to mutex" etc.

And the explanation (which is the only I can find, still cannot
explain very well the reason for the conversion IMHO) is contained in
Documentation/mutex-design.txt).   But this documentation also
mentioned a lot of the dos and dont' about mutex.....read it....very
informative.

On Thu, Mar 6, 2008 at 9:50 PM, Lukas Razik <linux@xxxxxxxxxx> wrote:
> Hello again!
>
>
>
>  >> > mutex does not "lock" in the sense of blocking the CPU - but in the
>  >> > sense that if the lock is not free, the task will be switch out and
>  >> > another task switch in, done by scheduler.
>  >>
>  >> O.K. I understand so I ask in another way:
>  >> For example my work handler is running on CPU0 and holds the mutex_lock.
>  >> Then (on CPU1) my work handler also calls mutex_lock.
>  >> Will it "see" that the lock is held by the work handler on CPU0 and will
>  >> it be switched out by the scheduler?
>  >>
>  >
>  >
>  > I think one answer can answer both question:   Generally, all locking
>  > API always work on global variable.   Global variable means the entire
>  > linux kernel only have one copy of the variable. For eg, for varA all
>  > spinlock(varA) are basically holding on the same variable - the same
>  > copy in memory.
>  >
>  > There is no meaning of individual CPU have their own private variable
>  > - individually whatever they do, is not visible to the other CPU, so
>  > what is the purpose of locking?
>  >
>  > Yes, all API means semaphore/mutex/spinlocks.
>  >
>
>  O.K. So I use mutex_locks now.
>  Many Thanks for the information and your patience!
>
>  Regards,
>  Lukas
>



-- 
Regards,
Peter Teoh

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