From cf8ff0e71369afdf600e36924c2d046ecf783cbf Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Sun, 18 Oct 2020 02:51:32 +0200
Subject: 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.
---
 sys/src/9/pc/sdnvme.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/sys/src/9/pc/sdnvme.c b/sys/src/9/pc/sdnvme.c
index 152dba187..1909eabdb 100644
--- a/sys/src/9/pc/sdnvme.c
+++ b/sys/src/9/pc/sdnvme.c
@@ -41,6 +41,7 @@ struct SQ
 	u32int	*base;
 	WS	**wait;
 	Ctlr	*ctlr;
+	Lock;
 };
 
 struct Ctlr
@@ -63,6 +64,8 @@ struct Ctlr
 	u32int	mpsshift;
 	u32int	dstrd;
 
+	u32int	nsq;
+
 	CQ	cq[1+1];
 	SQ	sq[1+MAXMACH];
 
@@ -99,7 +102,9 @@ qcmd(WS *ws, Ctlr *ctlr, int adm, u32int opc, u32int nsid, void *mptr, void *dat
 	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 @@ wcmd(WS *ws)
 	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 @@ sqalloc(Ctlr *ctlr, SQ *sq, u32int lgsize)
 static void
 setupqueues(Ctlr *ctlr)
 {
-	u32int lgsize, *e;
+	u32int lgsize, st, *e;
 	CQ *cq;
 	SQ *sq;
 	WS ws;
@@ -400,6 +407,8 @@ setupqueues(Ctlr *ctlr)
 	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 @@ setupqueues(Ctlr *ctlr)
 		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 @@ nvmeenable(SDev *sd)
 Ready:
 	identify(ctlr);
 	setupqueues(ctlr);
-
+	print("%s: using %d submit queues\n", name, ctlr->nsq);
 	poperror();
 
 	return 1;
-- 
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