Date: Wed, 22 Jan 2014 12:59:37 -0800 From: Alfred Perlstein <alfred@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: src-committers@freebsd.org, Scott Long <scott4long@yahoo.com>, Neel Natu <neel@freebsd.org>, John-Mark Gurney <jmg@funkthat.com>, svn-src-all@freebsd.org, Rui Paulo <rpaulo@felyko.com>, svn-src-head@freebsd.org, Alexander Kabaev <kabaev@gmail.com> Subject: Re: svn commit: r260898 - head/sys/kern Message-ID: <52E03139.2020902@freebsd.org> In-Reply-To: <201401221527.12779.jhb@freebsd.org> References: <201401200159.s0K1xa5X012123@svn.freebsd.org> <20140122181443.GU75135@funkthat.com> <52E016BF.80102@freebsd.org> <201401221527.12779.jhb@freebsd.org>
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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
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