Some doubts on MUTEX

[subin gangadharan]

On Tue, Feb 22, 2011 at 3:20 PM, Dave Hylands <dhylands at gmail.com> wrote:

> Hi Subin,
>
> On Tue, Feb 22, 2011 at 4:00 PM, subin gangadharan
> <subingangadharan at gmail.com> wrote:
> > Hi All,
> > I am trying to understand how to use mutex API's properly,so while going
> > through the documentation,
> > there is section mentioning fast path and slow path for mutexes.
> > For your reference I am pasting this here.(kernel/mutex.c)
> > /*
> >  * We split the mutex lock/unlock logic into separate fastpath and
> >  * slowpath functions, to reduce the register pressure on the fastpath.
> >  * We also put the fastpath first in the kernel image, to make sure the
> >  * branch is predicted by the CPU as default-untaken.
> >  */
> > static __used noinline void __sched
> > __mutex_lock_slowpath(atomic_t *lock_count);
> >
> > Can someone help me to understand what is the difference between fastpath
> > lock and slowpath lock?
>
> The fastpath is taken when nobody else is holding the lock (so the
> caller acquires the mutex without blocking).
>
> The slowpath is taken when somebody else is holding the lock and the
> caller needs to block (i.e. sleep) until the mutex is released.
>
> Thanks David.
Could you give a bit more idea on the "How this reduce the register pressure
on fast path"


> Dave Hyland
>




-- 
With Regards
Subin Gangadharan

Everything should be made as simple as possible,but not simpler.
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