Re: [PATCH gnumach] Enable MACH_HOST and fix non-addressable bitfields

[Damien Zammit]

Hi,

On 2/11/24 9:43 PM, Samuel Thibault wrote:

> Damien Zammit, le dim. 11 févr. 2024 07:09:48 +0000, a ecrit:
>> diff --git a/configfrag.ac b/configfrag.ac
>> index f9285c9d..d059c7b9 100644
>> --- a/configfrag.ac
>> +++ b/configfrag.ac
>> @@ -71,7 +71,7 @@ AC_DEFINE([MACH_DEBUG], [1], [MACH_DEBUG])
>>   AC_DEFINE([MACH_FIXPRI], [1], [MACH_FIXPRI])
>>
>>   # Mach host (resource alloc.).
>> -AC_DEFINE([MACH_HOST], [0], [MACH_HOST])
>> +AC_DEFINE([MACH_HOST], [1], [MACH_HOST])
> That's enabling a significant part of code. Better only enable it only
> for NCPUS > 1

OK that is fair.

>> 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.

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?

Damien