Date: Tue, 5 Aug 2003 17:15:17 -0700 (PDT) From: Julian Elischer <julian@elischer.org> To: Mike Makonnen <mtm@identd.net> Cc: Marcel Moolenaar <marcel@xcllnt.net> Subject: Re: cvs commit: src/sys/i386/i386 sys_machdep.c Message-ID: <Pine.BSF.4.21.0308051651070.82100-100000@InterJet.elischer.org> In-Reply-To: <20030805231633.GA24684@kokeb.ambesa.net>
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check the change Dan just checked in...
FreeBSD src repository
Modified files:
lib/libpthread/arch/i386/i386 pthread_md.c
Log:
Use auto LDT allocation for i386.
Revision Changes Path
1.2 +6 -63 src/lib/libpthread/arch/i386/i386/pthread_md.c
I have been thinking about this..
I assume you have some cached threads around, so you'd not be calling
this every time there is a new thread..
For KSE we only do this for a new KSE which is a less frequent
operation.
On Tue, 5 Aug 2003, Mike Makonnen wrote:
> On Sat, Aug 02, 2003 at 02:03:39PM -0700, Marcel Moolenaar wrote:
> > On Sat, Aug 02, 2003 at 03:52:44PM -0400, Mike Makonnen wrote:
> > >
> > > As I indicated to Julian, I don't have time to do this now. I will
> > > be going off-line in a couple of weeks for I don't know how long.
> > > In the mean time I have a bunch of other stuff I have to get to.
> > > But, if someone else wants to do it I can tell you exactly
> > > what you need to do. It's relatively simple.
> >
> > Can you post the description to threads@?
> > I'll see if I can find a spare moment...
>
> When I went back over the code, to write this summary
> I found it is going to be much easier than I thought
> at first. Assuming, i386_set_ldt() returns the auto-allocated
> LDT slot we just have to load that into %gs, instead of
> the ldt_index (which points into the ldt_entries array).
The value returned is the slot number so you need to
<< by 3 and set the Local bit for a legit value for %gs
It is the same value that was returned before except that the kernel
choses it for you if you specify a location of LDT_AUTO_ALLOC
instead of a legal slot number.
(i.e. Do whatever you are doing now with
the return value before you put it into %gs.)
>
> So, if someone can tell me what the magic number for
> auto-allocation is I can take care of this tonight. But,
> because I'll be offline soon I'll go ahead and post
> the background on how that code works just in case someone
> needs to mess with it.
>
> The pointers to pthread structures are kept in the array
> ldt_entries[MAX_THR]. Currently, MAX_THR is set to 128, but
> since we start at index NLDT the maximum number of simultaneous
> threads in an application is MAX_THR - NLDT. The global variable
> ldt_free is used to keep track of the next free index in the
> array. To facilitate this, when libthr is first initialized
> each entry in the array contains a pointer to the next free
> index. The ldt_free variable is then set to point to the first
> free entry in the array (ldt_entries[NLDT]) and the contents
> of that index (as preveiously stated) will be a pointer to
> the next free entry in the array (in this case
> ldt_entries[NLDT + 1]). When a new pthread is created, ldt_free
> is dereferenced to find the next empty entry. It is set to this
> entry and the contents of the previous entry it pointed to
> are overwritten with the address of the newly created pthread.
> When a thread exits the array index it occupied is overwritten
> by a pointer to ldt_free and ldt_free is pointed to the
> array index that held the just freed pthread.
>
> Another thing that happens when a new pthread is created is that
> we setup a segment descriptor structure which points into the
> ldt_entries entry we just setup for our newly created pthread.
> This segment descripter pointing into ldt_entries is what is
> passed into i386_set_ldt(). If the call to i386_set_ldt() succeeds
> we then load the LDT index into %gs.
>
> So, there should be no need to bump up any limits or anything
> to accomodate this change.
>
> Cheers.
> --
> Mike Makonnen | GPG-KEY: http://www.identd.net/~mtm/mtm.asc
> mtm@identd.net | D228 1A6F C64E 120A A1C9 A3AA DAE1 E2AF DBCC 68B9
> mtm@FreeBSD.Org| FreeBSD - Unleash the Daemon!
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