linux/kernel/sched.c: context_switch().

linux/kernel/sched.c: context_switch().

[fabio de francesco]

There must be something I am missing in sched.c at context_switch() function 
definition. 

There I can read the following code:

static inline void
context_switch(struct rq *rq, struct task_struct *prev,
               struct task_struct *next)
{
	...
	struct mm_struct *mm;
	mm = next->mm;
	if (likely(!mm)) {
                next->active_mm = oldmm;
                atomic_inc(&oldmm->mm_count);
                enter_lazy_tlb(oldmm, next);
        } else
                switch_mm(oldmm, mm, next);
	...
}

May someone please explain why the mm pointer is likely supposed to be NULL?

Thanks in advance.

fabio

Re: linux/kernel/sched.c: context_switch().

[chxanders]

Long day? Do you mean likely(!mm) actually means unlikely(0)?


On 8 September 2010 20:08, fabio de francesco <fabio@metanix.org> wrote:
> There must be something I am missing in sched.c at context_switch() function
> definition.
>
> There I can read the following code:
>
> static inline void
> context_switch(struct rq *rq, struct task_struct *prev,
>               struct task_struct *next)
> {
>        ...
>        struct mm_struct *mm;
>        mm = next->mm;
>        if (likely(!mm)) {
>                next->active_mm = oldmm;
>                atomic_inc(&oldmm->mm_count);
>                enter_lazy_tlb(oldmm, next);
>        } else
>                switch_mm(oldmm, mm, next);
>        ...
> }
>
> May someone please explain why the mm pointer is likely supposed to be NULL?
>
> Thanks in advance.
>
> fabio
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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>

Re: linux/kernel/sched.c: context_switch().

[fabio de francesco]

On Wednesday 08 September 2010 15:10:49 you wrote:
> Long day? Do you mean likely(!mm) actually means unlikely(0)?

No, no. I am sorry for my poor English. I mean:"likely(!mm)" is like 
"likely(0)".
 
> On 8 September 2010 20:08, fabio de francesco <fabio@metanix.org> wrote:
> > There must be something I am missing in sched.c at context_switch()
> > function definition.
> > 
> > There I can read the following code:
> > 
> > static inline void
> > context_switch(struct rq *rq, struct task_struct *prev,
> >               struct task_struct *next)
> > {
> >        ...
> >        struct mm_struct *mm;
> >        mm = next->mm;
> >        if (likely(!mm)) {
> >                next->active_mm = oldmm;
> >                atomic_inc(&oldmm->mm_count);
> >                enter_lazy_tlb(oldmm, next);
> >        } else
> >                switch_mm(oldmm, mm, next);
> >        ...
> > }
> > 
> > May someone please explain why the mm pointer is likely supposed to be
> > NULL?
> > 
> > Thanks in advance.
> > 
> > fabio
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel"
> > in the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/

Re: linux/kernel/sched.c: context_switch().

[fabio de francesco]

On Wednesday 08 September 2010 15:22:07 you wrote:
> but there is a ! not operator, !mm means mm != 0 , or the other way it
> is saying it is unlikey(mm is NULL)

Ok. Let me point to Linux-2.6.32. You may see that there the opposite is 
written. Can you please explain why they changed unlikely with likely passing 
from 2.6.32 to 2.6.33?

> On 8 September 2010 20:18, fabio de francesco <fabio@metanix.org> wrote:
> > On Wednesday 08 September 2010 15:10:49 you wrote:
> >> Long day? Do you mean likely(!mm) actually means unlikely(0)?
> > 
> > No, no. I am sorry for my poor English. I mean:"likely(!mm) is like
> > "likely(0)".
> > 
> >> On 8 September 2010 20:08, fabio de francesco <fabio@metanix.org> wrote:
> >> > There must be something I am missing in sched.c at context_switch()
> >> > function definition.
> >> > 
> >> > There I can read the following code:
> >> > 
> >> > static inline void
> >> > context_switch(struct rq *rq, struct task_struct *prev,
> >> >               struct task_struct *next)
> >> > {
> >> >        ...
> >> >        struct mm_struct *mm;
> >> >        mm = next->mm;
> >> >        if (likely(!mm)) {
> >> >                next->active_mm = oldmm;
> >> >                atomic_inc(&oldmm->mm_count);
> >> >                enter_lazy_tlb(oldmm, next);
> >> >        } else
> >> >                switch_mm(oldmm, mm, next);
> >> >        ...
> >> > }
> >> > 
> >> > May someone please explain why the mm pointer is likely supposed to be
> >> > NULL?
> >> > 
> >> > Thanks in advance.
> >> > 
> >> > fabio
> >> > --
> >> > To unsubscribe from this list: send the line "unsubscribe
> >> > linux-kernel" in the body of a message to majordomo@vger.kernel.org
> >> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >> > Please read the FAQ at  http://www.tux.org/lkml/

linux/kernel/sched.c: context_switch().

[fabio de francesco]

There must be something I am missing in sched.c at context_switch() function 
definition. 

There I can read the following code:

static inline void
context_switch(struct rq *rq, struct task_struct *prev,
               struct task_struct *next)
{
	...
	struct mm_struct *mm;
	mm = next->mm;
	if (likely(!mm)) {
                next->active_mm = oldmm;
                atomic_inc(&oldmm->mm_count);
                enter_lazy_tlb(oldmm, next);
        } else
                switch_mm(oldmm, mm, next);
	...
}

May someone please explain why the mm pointer is likely supposed to be NULL?

Thanks in advance.

fabio