From owner-freebsd-arch  Mon Nov 12 16:34:54 2001
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Date: Mon, 12 Nov 2001 16:34:52 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
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To: John Baldwin <jhb@FreeBSD.org>
Cc: freebsd-arch@FreeBSD.org, Robert Watson <rwatson@FreeBSD.org>,
	Terry Lambert <tlambert2@mindspring.com>
Subject: Re: cur{thread/proc}, or not.
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:is how does your pool work?  Do you pick a mutex out of the pool at init time
:like the lockmgr locks work?  Or do you use a hash on the object address?

    I was thinking non-chained hash on the object address.  Real simple.
    (((int)ptr >> 5) ^ (int)ptr) & MASK or something like that.  Or something
    even simpler... basically something we can play around with and optimize
    later without breaking the API we've constructed.

:Well, there are different ways of doing lock pools. :)  How about something
:like this:
:
:/*
: * Returns lock for address 'ptr'.
: *
:mtx_pool_find(void *ptr)
:{
:}
:
:#define mtx_pool_lock(p)        mtx_lock(mtx_pool_find((p)))
:#define mtx_pool_unlock(p)      mtx_unlock(mtx_pool_find((p))
:
:Then if a structure (like lockmgr locks or sx locks) wants to cache the lock
:pointer instead of doing the hash all the time, it can just do
:
:        foo->f_lock = mtx_pool_find(foo);
:
:This actually isn't all that difficult, it just adds the ability to lookup and
:cache the mutex associated with an address.  I would also like it under mtx_*
:so it's clear what type of locks are in the pool, but that's just me. :)

    Yes I think the addition of a mtx_pool_find() call is excellent!  A
    wonderful example of horizontal expansion (rather then vertical
    complexity, or vertical complication if I'm being cute).

						-Matt


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