Date: Sat, 14 Dec 1996 14:51:50 -0700 From: Steve Passe <smp@csn.net> To: Steve Passe <smp@csn.net> Cc: haertel@ichips.intel.com, peter@spinner.dialix.com, dg@root.com, smp@freebsd.org, toor@dyson.iquest.net Subject: Re: some questions concerning TLB shootdowns in FreeBSD Message-ID: <199612142151.OAA17577@clem.systemsix.com> In-Reply-To: Your message of "Sat, 14 Dec 1996 11:55:18 MST." <199612141855.LAA16724@clem.systemsix.com>
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Hi,
so here is a suggested set of code for the TLB sync problem. There is one
problem with it (that I currently see, surely others also!) in that the
target CPUs can't service their IPI as the invoking CPU holds the mp_lock.
So for now lets pretend that we have a separate lock for IPIs called
ipi_lock, which is manipulated via get_ipilock()/rel_ipilock().
---
usage by the invoking CPU:
startRendezvous(); /* setup a rendezvous */
/*
* at this point the other CPUs are all spinning on the end lock
* so the code can safely muck with PTD/PTE entries...
*/
invltlb(); /* CPU flushes local TLB */
endRendezvous(); /* end the rendezvous */
---
usage by the invoked CPUs, ie the routine invoked by the IPI:
ipi_invltlb(void)
{
u_long temp;
doRendezvous(); /* declare our arrival and wait */
__asm __volatile("movl %%cr3, %0; movl %0, %%cr3" : "=r" (temp)
: : "memory");
}
----------------------------------- cut -------------------------------------
/* rendezvous.s */
.text
.align 4
#define SMP_INVLTLB_IPI (ICU_OFFSET+27)
/*
* invoking CPU sets up rendezvous
*/
ENTRY(startRendezvous)
call _get_ipilock /* only one CPU at a time */
movl _mp_ncpus, %eax /* # of CPUs to sync */
decl %eax /* count ourself */
movl %eax, _rendezvousCount /* init the downcounter */
movl %eax, _rendezvousEnd /* init the release lock */
pushl SMP_INVLTLB_IPI
call _allButSelfIPI
addl $4, %esp
call _rel_ipilock /* now safe for other CPUs */
1: cmpl $0, _rendezvousCount /* check current value */
jnz 1b /* somebody not here yet */
call _get_ipilock /* is this necessary??? */
ret
/*
* invoking CPU releases all other CPUs
*/
ENTRY(endRendezvous)
movl $0, _rendezvousEnd
call _rel_ipilock /* is this necessary??? */
ret
/*
* invoked CPUs enter and wait for end
*/
ENTRY(doRendezvous)
call _rel_ipilock /* allow other CPUs to IPI */
lock /* ensure atomic operation */
decl _rendezvousCount /* declare our arrival */
1: cmpl $0, _rendezvousEnd /* test for end */
jnz 1b /* not yet, spin */
call _get_ipilock /* safe exit from IPI */
ret
.data
ALIGN_DATA
.globl _rendezvousCount
_rendezvousCount:
.long 0
.globl _rendezvousEnd
_rendezvousEnd:
.long 0
----------------------------------- cut -------------------------------------
--
Steve Passe | powered by
smp@csn.net | FreeBSD
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