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aoe: improve network congestion handling
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The aoe driver already had some congestion handling, but it was limited in
its ability to cope with the kind of congestion that can arise on more
complex networks such as those involving paths through multiple ethernet
switches.

Some of the lessons from TCP's history of development can be applied to
improving the congestion control and avoidance on AoE storage networks.
These changes use familar concepts from Van Jacobson's "Congestion
Avoidance and Control" paper from '88, without adding significant
overhead.

This patch depends on an upcoming patch that covers the failover case when
AoE commands being retransmitted are transferred from one retransmit queue
to another.  Another upcoming patch increases the timing accuracy.

Signed-off-by: Ed Cashin <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Ed Cashin authored and Linus Torvalds committed Dec 18, 2012
1 parent 667be1e commit 3a0c40d
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Showing 3 changed files with 121 additions and 74 deletions.
16 changes: 11 additions & 5 deletions drivers/block/aoe/aoe.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -86,8 +86,11 @@ enum {
NFACTIVE = 61,

TIMERTICK = HZ / 10,
MINTIMER = HZ >> 2,
RTTSCALE = 8,
RTTDSCALE = 3,
MAXTIMER = HZ << 1,
RTTAVG_INIT = HZ / 4 << RTTSCALE,
RTTDEV_INIT = RTTAVG_INIT / 4,
};

struct buf {
Expand Down Expand Up @@ -127,10 +130,11 @@ struct aoetgt {
struct list_head ffree; /* list of free frames */
struct aoeif ifs[NAOEIFS];
struct aoeif *ifp; /* current aoeif in use */
ushort nout;
ushort nout; /* value of nout when skb was sent */
ushort maxout; /* current value for max outstanding */
ushort next_cwnd; /* incr maxout after decrementing to zero */
ushort ssthresh; /* slow start threshold */
ulong falloc; /* number of allocated frames */
ulong lastwadj; /* last window adjustment */
int minbcnt;
int wpkts, rpkts;
};
Expand All @@ -142,8 +146,8 @@ struct aoedev {
u16 aoeminor;
u16 flags;
u16 nopen; /* (bd_openers isn't available without sleeping) */
u16 rttavg; /* round trip average of requests/responses */
u16 mintimer;
u16 rttavg; /* scaled AoE round trip time average */
u16 rttdev; /* scaled round trip time mean deviation */
u16 fw_ver; /* version of blade's firmware */
u16 lasttag; /* last tag sent */
u16 useme;
Expand All @@ -164,6 +168,7 @@ struct aoedev {
} ip;
ulong maxbcnt;
struct list_head factive[NFACTIVE]; /* hash of active frames */
struct list_head rexmitq; /* deferred retransmissions */
struct aoetgt *targets[NTARGETS];
struct aoetgt **tgt; /* target in use when working */
struct aoetgt *htgt; /* target needing rexmit assistance */
Expand Down Expand Up @@ -196,6 +201,7 @@ void aoecmd_cfg(ushort aoemajor, unsigned char aoeminor);
struct sk_buff *aoecmd_ata_rsp(struct sk_buff *);
void aoecmd_cfg_rsp(struct sk_buff *);
void aoecmd_sleepwork(struct work_struct *);
void aoecmd_wreset(struct aoetgt *t);
void aoecmd_cleanslate(struct aoedev *);
void aoecmd_exit(void);
int aoecmd_init(void);
Expand Down
173 changes: 106 additions & 67 deletions drivers/block/aoe/aoecmd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,23 @@ new_skb(ulong len)
return skb;
}

static struct frame *
getframe_deferred(struct aoedev *d, u32 tag)
{
struct list_head *head, *pos, *nx;
struct frame *f;

head = &d->rexmitq;
list_for_each_safe(pos, nx, head) {
f = list_entry(pos, struct frame, head);
if (f->tag == tag) {
list_del(pos);
return f;
}
}
return NULL;
}

static struct frame *
getframe(struct aoedev *d, u32 tag)
{
Expand Down Expand Up @@ -552,11 +569,30 @@ sthtith(struct aoedev *d)
return 1;
}

static void
rexmit_deferred(struct aoedev *d)
{
struct aoetgt *t;
struct frame *f;
struct list_head *pos, *nx, *head;

head = &d->rexmitq;
list_for_each_safe(pos, nx, head) {
f = list_entry(pos, struct frame, head);
t = f->t;
if (t->nout >= t->maxout)
continue;
list_del(pos);
t->nout++;
resend(d, f);
}
}

static void
rexmit_timer(ulong vp)
{
struct aoedev *d;
struct aoetgt *t, **tt, **te;
struct aoetgt *t;
struct aoeif *ifp;
struct frame *f;
struct list_head *head, *pos, *nx;
Expand All @@ -567,9 +603,11 @@ rexmit_timer(ulong vp)

d = (struct aoedev *) vp;

/* timeout is always ~150% of the moving average */
timeout = d->rttavg;
timeout += timeout >> 1;
/* timeout based on observed timings and variations */
timeout = 2 * d->rttavg >> RTTSCALE;
timeout += 8 * d->rttdev >> RTTDSCALE;
if (timeout == 0)
timeout = 1;

spin_lock_irqsave(&d->lock, flags);

Expand All @@ -589,29 +627,12 @@ rexmit_timer(ulong vp)
list_move_tail(pos, &flist);
}
}
/* window check */
tt = d->targets;
te = tt + d->ntargets;
for (; tt < te && (t = *tt); tt++) {
if (t->nout == t->maxout
&& t->maxout < t->nframes
&& (jiffies - t->lastwadj)/HZ > 10) {
t->maxout++;
t->lastwadj = jiffies;
}
}

if (!list_empty(&flist)) { /* retransmissions necessary */
n = d->rttavg <<= 1;
if (n > MAXTIMER)
d->rttavg = MAXTIMER;
}

/* process expired frames */
while (!list_empty(&flist)) {
pos = flist.next;
f = list_entry(pos, struct frame, head);
n = f->waited += timeout;
n = f->waited += tsince(f->tag);
n /= HZ;
if (n > aoe_deadsecs) {
/* Waited too long. Device failure.
Expand All @@ -620,18 +641,16 @@ rexmit_timer(ulong vp)
*/
list_splice(&flist, &d->factive[0]);
aoedev_downdev(d);
break;
goto out;
}
list_del(pos);

t = f->t;
if (n > aoe_deadsecs/2)
d->htgt = t; /* see if another target can help */

if (t->nout == t->maxout) {
if (t->maxout > 1)
t->maxout--;
t->lastwadj = jiffies;
if (t->maxout != 1) {
t->ssthresh = t->maxout / 2;
t->maxout = 1;
}

ifp = getif(t, f->skb->dev);
Expand All @@ -640,9 +659,12 @@ rexmit_timer(ulong vp)
ejectif(t, ifp);
ifp = NULL;
}
resend(d, f);
list_move_tail(pos, &d->rexmitq);
t->nout--;
}
rexmit_deferred(d);

out:
if ((d->flags & DEVFL_KICKME || d->htgt) && d->blkq) {
d->flags &= ~DEVFL_KICKME;
d->blkq->request_fn(d->blkq);
Expand Down Expand Up @@ -766,6 +788,7 @@ aoecmd_work(struct aoedev *d)
{
if (d->htgt && !sthtith(d))
return;
rexmit_deferred(d);
while (aoecmd_ata_rw(d))
;
}
Expand Down Expand Up @@ -868,26 +891,28 @@ ataid_complete(struct aoedev *d, struct aoetgt *t, unsigned char *id)
}

static void
calc_rttavg(struct aoedev *d, int rtt)
calc_rttavg(struct aoedev *d, struct aoetgt *t, int rtt)
{
register long n;

n = rtt;
if (n < 0) {
n = -rtt;
if (n < MINTIMER)
n = MINTIMER;
else if (n > MAXTIMER)
n = MAXTIMER;
d->mintimer += (n - d->mintimer) >> 1;
} else if (n < d->mintimer)
n = d->mintimer;
else if (n > MAXTIMER)
n = MAXTIMER;

/* g == .25; cf. Congestion Avoidance and Control, Jacobson & Karels; 1988 */
n -= d->rttavg;
d->rttavg += n >> 2;

/* cf. Congestion Avoidance and Control, Jacobson & Karels, 1988 */
n -= d->rttavg >> RTTSCALE;
d->rttavg += n;
if (n < 0)
n = -n;
n -= d->rttdev >> RTTDSCALE;
d->rttdev += n;

if (!t || t->maxout >= t->nframes)
return;
if (t->maxout < t->ssthresh)
t->maxout += 1;
else if (t->nout == t->maxout && t->next_cwnd-- == 0) {
t->maxout += 1;
t->next_cwnd = t->maxout;
}
}

static struct aoetgt *
Expand Down Expand Up @@ -1147,7 +1172,6 @@ aoecmd_ata_rsp(struct sk_buff *skb)
struct aoedev *d;
struct aoe_hdr *h;
struct frame *f;
struct aoetgt *t;
u32 n;
ulong flags;
char ebuf[128];
Expand All @@ -1168,23 +1192,28 @@ aoecmd_ata_rsp(struct sk_buff *skb)

n = be32_to_cpu(get_unaligned(&h->tag));
f = getframe(d, n);
if (f == NULL) {
calc_rttavg(d, -tsince(n));
spin_unlock_irqrestore(&d->lock, flags);
aoedev_put(d);
snprintf(ebuf, sizeof ebuf,
"%15s e%d.%d tag=%08x@%08lx\n",
"unexpected rsp",
get_unaligned_be16(&h->major),
h->minor,
get_unaligned_be32(&h->tag),
jiffies);
aoechr_error(ebuf);
return skb;
if (f) {
calc_rttavg(d, f->t, tsince(n));
f->t->nout--;
} else {
f = getframe_deferred(d, n);
if (f) {
calc_rttavg(d, NULL, tsince(n));
} else {
calc_rttavg(d, NULL, tsince(n));
spin_unlock_irqrestore(&d->lock, flags);
aoedev_put(d);
snprintf(ebuf, sizeof(ebuf),
"%15s e%d.%d tag=%08x@%08lx\n",
"unexpected rsp",
get_unaligned_be16(&h->major),
h->minor,
get_unaligned_be32(&h->tag),
jiffies);
aoechr_error(ebuf);
return skb;
}
}
t = f->t;
calc_rttavg(d, tsince(f->tag));
t->nout--;
aoecmd_work(d);

spin_unlock_irqrestore(&d->lock, flags);
Expand Down Expand Up @@ -1241,7 +1270,8 @@ aoecmd_ata_id(struct aoedev *d)

skb->dev = t->ifp->nd;

d->rttavg = MAXTIMER;
d->rttavg = RTTAVG_INIT;
d->rttdev = RTTDEV_INIT;
d->timer.function = rexmit_timer;

return skb_clone(skb, GFP_ATOMIC);
Expand Down Expand Up @@ -1273,7 +1303,7 @@ addtgt(struct aoedev *d, char *addr, ulong nframes)
t->d = d;
memcpy(t->addr, addr, sizeof t->addr);
t->ifp = t->ifs;
t->maxout = t->nframes;
aoecmd_wreset(t);
INIT_LIST_HEAD(&t->ffree);
return *tt = t;
}
Expand Down Expand Up @@ -1382,7 +1412,7 @@ aoecmd_cfg_rsp(struct sk_buff *skb)
if (t) {
t->nframes = n;
if (n < t->maxout)
t->maxout = n;
aoecmd_wreset(t);
} else {
t = addtgt(d, h->src, n);
if (!t)
Expand Down Expand Up @@ -1411,18 +1441,27 @@ aoecmd_cfg_rsp(struct sk_buff *skb)
}
}

void
aoecmd_wreset(struct aoetgt *t)
{
t->maxout = 1;
t->ssthresh = t->nframes / 2;
t->next_cwnd = t->nframes;
}

void
aoecmd_cleanslate(struct aoedev *d)
{
struct aoetgt **t, **te;

d->mintimer = MINTIMER;
d->rttavg = RTTAVG_INIT;
d->rttdev = RTTDEV_INIT;
d->maxbcnt = 0;

t = d->targets;
te = t + NTARGETS;
for (; t < te && *t; t++)
(*t)->maxout = (*t)->nframes;
aoecmd_wreset(*t);
}

void
Expand Down
6 changes: 4 additions & 2 deletions drivers/block/aoe/aoedev.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -198,7 +198,7 @@ aoedev_downdev(struct aoedev *d)
tt = d->targets;
te = tt + NTARGETS;
for (; tt < te && (t = *tt); tt++) {
t->maxout = t->nframes;
aoecmd_wreset(t);
t->nout = 0;
}

Expand Down Expand Up @@ -391,10 +391,12 @@ aoedev_by_aoeaddr(ulong maj, int min, int do_alloc)
d->ref = 1;
for (i = 0; i < NFACTIVE; i++)
INIT_LIST_HEAD(&d->factive[i]);
INIT_LIST_HEAD(&d->rexmitq);
d->sysminor = sysminor;
d->aoemajor = maj;
d->aoeminor = min;
d->mintimer = MINTIMER;
d->rttavg = RTTAVG_INIT;
d->rttdev = RTTDEV_INIT;
d->next = devlist;
devlist = d;
out:
Expand Down

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