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kernel: avoid useless mmu flushes, implement better wait condition for procflushmmu()

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procflushmmu() returns once all *OTHER* processors that had
matching processes running on them flushed ther tlb/mmu state.
the caller of procflush...() takes care of flushing "up" by
calling flushmmu() later.

if the current process matched, then that means m->flushmmu
would be set, and hzclock() would call flushmmu() again.

to avoid this, we now check up->newtlb in addition to m->flushmmu
in hzclock() before calling flushmmu().

we also maintain information on which process on what processor
to wait for locally, which helps making progress when multiple
procflushmmu()'s are running concurrently.

in addition, this makes the wait condition for procflushmmu()
more sophisticated, by validating if the processor still runs
the selected process and only if it matchatches, considers
the MACHP(nm)->flushmmu flag.
This commit is contained in:
cinap_lenrek 2019-12-07 02:13:51 +01:00
parent 480d7b8f5f
commit 28836f3ff5
2 changed files with 22 additions and 9 deletions
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2
sys/src/9/port/portclock.c
View file

@ -148,7 +148,7 @@ hzclock(Ureg *ur)
m->proc->pc = ur->pc;
if(m->flushmmu){
if(up)
if(up && up->newtlb)
flushmmu();
m->flushmmu = 0;
}

29
sys/src/9/port/proc.c
View file

@ -1331,36 +1331,49 @@ procdump(void)
static void
procflushmmu(int (*match)(Proc*, void*), void *a)
{
Proc *await[MAXMACH];
int i, nm, nwait;
Proc *p;
/*
* tell all matching processes to flush their mmu's
*/
memset(await, 0, conf.nmach*sizeof(await[0]));
nwait = 0;
for(i=0; i<conf.nproc; i++) {
for(i = 0; i < conf.nproc; i++){
p = &procalloc.arena[i];
if(p->state != Dead && (*match)(p, a)){
p->newtlb = 1;
for(nm = 0; nm < conf.nmach; nm++){
if(MACHP(nm)->proc == p){
coherence();
MACHP(nm)->flushmmu = 1;
nwait++;
if(await[nm] == nil)
nwait++;
await[nm] = p;
}
}
}
}
if(nwait == 0)
return;
/*
* wait for all other processors to take a clock interrupt
* and flush their mmu's
*/
for(nm = 0; nm < conf.nmach; nm++)
while(m->machno != nm && MACHP(nm)->flushmmu)
sched();
for(;;){
if(nwait == 0 || nwait == 1 && await[m->machno] != nil)
break;
sched();
for(nm = 0; nm < conf.nmach; nm++){
p = await[nm];
if(p != nil && (MACHP(nm)->proc != p || MACHP(nm)->flushmmu == 0)){
await[nm] = nil;
nwait--;
}
}
}
}
static int