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sdnvme: handle machines with more cpu's than submit queues (thanks mischief)

We used to assume a 1:1 pairing of processors to submit queues.
With recent machines, we now got more cpu cores than what some
nvme drives support so we need to distribute the queues across
these cpu's which requires locking on command submission.

There is a feature get/set command to probe the number of submit
and completion queues, but we decided to just handling
submission queue create command error gracefully as it is simpler
and has less chance of regression with existing setups.

Thanks to mischief for investigating and writing the code.

--- a/sys/src/9/pc/sdnvme.c

+++ b/sys/src/9/pc/sdnvme.c

@@ -41,6 +41,7 @@

 	u32int	*base;

 	WS	**wait;

 	Ctlr	*ctlr;

+	Lock;

 };

 struct Ctlr

@@ -63,6 +64,8 @@

 	u32int	mpsshift;

 	u32int	dstrd;

+	u32int	nsq;

+

 	CQ	cq[1+1];

 	SQ	sq[1+MAXMACH];

@@ -99,7 +102,9 @@

 	if(!adm){

 	Retry:

 		splhi();

-		sq = &ctlr->sq[1+m->machno];

+		sq = &ctlr->sq[1+(m->machno % ctlr->nsq)];

+		if(conf.nmach > ctlr->nsq)

+			lock(sq);

 	} else {

 		qlock(ctlr);

 		sq = &ctlr->sq[0];

@@ -207,7 +212,9 @@

 	coherence();

 	ctlr->reg[DBell + ((sq-ctlr->sq)*2+0 << ctlr->dstrd)] = sq->tail & sq->mask;

 	if(sq > ctlr->sq) {

-		assert(sq == &ctlr->sq[1+m->machno]);

+		assert(sq == &ctlr->sq[1+(m->machno % ctlr->nsq)]);

+		if(conf.nmach > ctlr->nsq)

+			unlock(sq);

 		spllo();

 	} else

 		qunlock(sq->ctlr);

@@ -381,7 +388,7 @@

 static void

 setupqueues(Ctlr *ctlr)

 {

-	u32int lgsize, *e;

+	u32int lgsize, st, *e;

 	CQ *cq;

 	SQ *sq;

 	WS ws;

@@ -400,6 +407,8 @@

 	e[11] = 3; /* IEN | PC */

 	checkstatus(wcmd(&ws), "create completion queue");

+	st = 0;

+

 	/* SQID[1..nmach]: submission queue per cpu */

 	for(i=1; i<=conf.nmach; i++){

 		sq = &ctlr->sq[i];

@@ -407,8 +416,19 @@

 		e = qcmd(&ws, ctlr, 1, 0x01, 0, nil, sq->base, 0x1000);

 		e[10] = i | sq->mask<<16;

 		e[11] = (cq - ctlr->cq)<<16 | 1;	/* CQID<<16 | PC */

-		checkstatus(wcmd(&ws), "create submission queue");

+

+		st = wcmd(&ws);

+		if(st != 0){

+			free(sq->base);

+			free(sq->wait);

+			memset(sq, 0, sizeof(*sq));

+			break;

+		}

 	}

+	

+	ctlr->nsq = i - 1;

+	if(ctlr->nsq < 1)

+		checkstatus(st, "create submission queues");

 	ilock(&ctlr->intr);

 	ctlr->ints |= 1<<(cq - ctlr->cq);

@@ -544,7 +564,7 @@

 Ready:

 	identify(ctlr);

 	setupqueues(ctlr);

-

+	print("%s: using %d submit queues\n", name, ctlr->nsq);

 	poperror();

 	return 1;