Samuel Thibault, le dim. 11 févr. 2024 15:01:43 +0100, a ecrit:
> Damien Zammit, le dim. 11 févr. 2024 11:30:31 +0000, a ecrit:
> > On 2/11/24 10:07 PM, Samuel Thibault wrote:
> > > Damien Zammit, le dim. 11 févr. 2024 10:55:26 +0000, a ecrit:
> > >>>> diff --git a/kern/task.h b/kern/task.h
> > >>>> index dec3a530..27970620 100644
> > >>>> --- a/kern/task.h
> > >>>> +++ b/kern/task.h
> > >>>> @@ -61,11 +61,11 @@ struct task {
> > >>>> decl_simple_lock_data(,lock) /* Task's lock */
> > >>>> int ref_count; /* Number of references to me */
> > >>>>
> > >>>> - /* Flags */
> > >>>> - unsigned int active:1, /* Task has not been terminated
> > >>>> */
> > >>>> - /* boolean_t */ may_assign:1, /* can assigned pset be
> > >>>> changed? */
> > >>>> - assign_active:1, /* waiting for
> > >>>> may_assign */
> > >>>> - essential:1; /* Is this task essential for
> > >>>> the system? */
> > >>>> + /* Addressable flags */
> > >>>> + unsigned char active; /* Task has not been terminated
> > >>>> */
> > >>>> + unsigned char may_assign; /* can assigned pset be
> > >>>> changed? */
> > >>>> + unsigned char assign_active; /* waiting for may_assign */
> > >>>> + unsigned char essential; /* Is this task essential for
> > >>>> the system? */
> > >>> AIUI only assign_active need to be adressable? Better make only that one
> > >>> addressable.
> > >> Looking at the existing flag types, it needs to fit into part of a
> > >> cacheline.
> > > Why would it need to fit in a cacheline?
> >
> > See comment above struct task:
> >
> > /*
> > * Task name buffer size. The size is chosen so that struct task fits
> > * into three cache lines. The size of a cache line on a typical CPU
> > * is 64 bytes.
> > */
> > #define TASK_NAME_SIZE 32
>
> Ok, but that's only for optimization.
>
> > >> The way I have done it, I rearranged the existing 4 byte integer to be 4
> > >> separate single byte flags.
> > >> If you want me to put only one of the values into an addressable field,
> > >> how will I retain the same size for the rest of the fields?
> > > What do you mean by "the same size"?
> >
> > I think the actual sizeof(struct task) and its layout matters.
>
> Ok
>
> > Therefore, my original code change here preserves most of the layout and
> > sizeof(struct task).
>
> The original code uses 4 bits, so a byte. Your proposed change uses 4
> bytes, so 3 more bytes. By using e.g.
>
> unsigned char may_assign, /* can assigned pset be changed? */
> unsigned int active:1, /* Task has not been terminated */
I meant unsigned char here of course.
> assign_active:1, /* waiting for may_assign */
> essential:1; /* Is this task essential for the
> system? */
>
> That'll be 2 bytes, so even better for cache line size.
>
> Samuel
>
--
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.
