svn commit: r260898 - head/sys/kern

[Alfred Perlstein]

On 1/22/14, 12:27 PM, John Baldwin wrote:
> On Wednesday, January 22, 2014 2:06:39 pm Alfred Perlstein wrote:
>> Hmm, what if locks had a pointer to a 2 element char * array, the first
>> being the name, the second the type.  That would keep the size of the
>> lock down and most locks could share a common tuple of name/type in each
>> subsystem.  This would allow us to get rid of the pending static list.
>>
>> effectively:
>> struct lock_object {
>>           char *lo_name;          /* Individual lock name. */
>>           u_int   lo_flags;
>>           u_int   lo_data;                /* General class specific data. */
>>           struct  witness *lo_witness;    /* Data for witness. */
>> };
>>
>> would change to:
>> struct lock_object {
>>           char **lo_name_type;          /* Individual lock
>> name[0]/type[1]. */
>>           u_int   lo_flags;
>>           u_int   lo_data;                /* General class specific data. */
>>           struct  witness *lo_witness;    /* Data for witness. */
>> };
>>
>> This may be somewhat disruptive, I haven't played with how it would
>> actually change driver/etc/code.
> Where would the memory for the char* array come from?
>
That is a good question.  I suspect it would be up to the subsystem to 
allocate it.

Wouldn't it be trivial for *most* of the subsystems to simply have this 
either as a static global or static function variable:

static char *mutex_typename = { "kqueue", "foo" };

Under kern I see this:
grep mtx_init * | grep -v NULL
...
kern_rmlock.c:        mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx", 
MTX_NOWITNESS);
subr_bus.c:    mtx_init(&devsoftc.mtx, "dev mtx", "devd", MTX_DEF);

Those are solved with statics.

Another example:

sys/dev/ae/if_ae.c
         mtx_init(&sc->mtx, device_get_nameunit(dev), MTX_NETWORK_LOCK, 
MTX_DEF);

I think the array could be in the softc here? sc->mutex_name_type[0] = 
device_get_nameunit(dev); sc->mutex_name_type[1] = MTX_NETWORK_LOCK;

Do we want to do that?  It moves "wasting space" to another variable.

I'm not sure where there isn't the possibility of using either static 
(for a global mutex) or space inside the equiv of the softc (or proc or 
whatever) for this?

I'm not sure this is a good idea, just an idea.  Are there places where 
it's not as simple as doing this?

-Alfred