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Message-Id: <846b893d27939c10c4f49a8e4d22f0029bebbd20.1352410985.git.ecashin@coraid.com>
Date: Thu, 8 Nov 2012 19:27:17 -0500
From: Ed Cashin <ecashin@...aid.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, ecashin@...aid.com
Subject: [PATCH 6/8] aoe: use high-resolution RTTs with fallback to low-res
These changes improve the accuracy of the decision about whether
it's time to retransmit an AoE command by using the
microsecond-resolution gettimeofday instead of jiffies.
Because the system time can jump suddenly, the decision reverts
to using jiffies if the high-resolution time difference is
relatively large. Otherwise the AoE targets could be considered
failed inappropriately.
Signed-off-by: Ed Cashin <ecashin@...aid.com>
---
drivers/block/aoe/aoe.h | 9 ++++---
drivers/block/aoe/aoecmd.c | 57 ++++++++++++++++++++++++++++++++++++++-----
2 files changed, 55 insertions(+), 11 deletions(-)
diff --git a/drivers/block/aoe/aoe.h b/drivers/block/aoe/aoe.h
index 9e884ac..9fb68fc 100644
--- a/drivers/block/aoe/aoe.h
+++ b/drivers/block/aoe/aoe.h
@@ -88,8 +88,7 @@ enum {
TIMERTICK = HZ / 10,
RTTSCALE = 8,
RTTDSCALE = 3,
- MAXTIMER = HZ << 1,
- RTTAVG_INIT = HZ / 4 << RTTSCALE,
+ RTTAVG_INIT = USEC_PER_SEC / 4 << RTTSCALE,
RTTDEV_INIT = RTTAVG_INIT / 4,
};
@@ -106,6 +105,8 @@ struct buf {
struct frame {
struct list_head head;
u32 tag;
+ struct timeval sent; /* high-res time packet was sent */
+ u32 sent_jiffs; /* low-res jiffies-based sent time */
ulong waited;
struct aoetgt *t; /* parent target I belong to */
sector_t lba;
@@ -143,11 +144,11 @@ struct aoedev {
struct aoedev *next;
ulong sysminor;
ulong aoemajor;
+ u32 rttavg; /* scaled AoE round trip time average */
+ u32 rttdev; /* scaled round trip time mean deviation */
u16 aoeminor;
u16 flags;
u16 nopen; /* (bd_openers isn't available without sleeping) */
- 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;
diff --git a/drivers/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c
index 9aefbe3..a99220a 100644
--- a/drivers/block/aoe/aoecmd.c
+++ b/drivers/block/aoe/aoecmd.c
@@ -387,6 +387,8 @@ aoecmd_ata_rw(struct aoedev *d)
skb->dev = t->ifp->nd;
skb = skb_clone(skb, GFP_ATOMIC);
if (skb) {
+ do_gettimeofday(&f->sent);
+ f->sent_jiffs = (u32) jiffies;
__skb_queue_head_init(&queue);
__skb_queue_tail(&queue, skb);
aoenet_xmit(&queue);
@@ -475,12 +477,46 @@ resend(struct aoedev *d, struct frame *f)
skb = skb_clone(skb, GFP_ATOMIC);
if (skb == NULL)
return;
+ do_gettimeofday(&f->sent);
+ f->sent_jiffs = (u32) jiffies;
__skb_queue_head_init(&queue);
__skb_queue_tail(&queue, skb);
aoenet_xmit(&queue);
}
static int
+tsince_hr(struct frame *f)
+{
+ struct timeval now;
+ int n;
+
+ do_gettimeofday(&now);
+ n = now.tv_usec - f->sent.tv_usec;
+ n += (now.tv_sec - f->sent.tv_sec) * USEC_PER_SEC;
+
+ if (n < 0)
+ n = -n;
+
+ /* For relatively long periods, use jiffies to avoid
+ * discrepancies caused by updates to the system time.
+ *
+ * On system with HZ of 1000, 32-bits is over 49 days
+ * worth of jiffies, or over 71 minutes worth of usecs.
+ *
+ * Jiffies overflow is handled by subtraction of unsigned ints:
+ * (gdb) print (unsigned) 2 - (unsigned) 0xfffffffe
+ * $3 = 4
+ * (gdb)
+ */
+ if (n > USEC_PER_SEC / 4) {
+ n = ((u32) jiffies) - f->sent_jiffs;
+ n *= USEC_PER_SEC / HZ;
+ }
+
+ return n;
+}
+
+static int
tsince(u32 tag)
{
int n;
@@ -489,7 +525,7 @@ tsince(u32 tag)
n -= tag & 0xffff;
if (n < 0)
n += 1<<16;
- return n;
+ return jiffies_to_usecs(n + 1);
}
static struct aoeif *
@@ -552,6 +588,7 @@ sthtith(struct aoedev *d)
nf->bv = f->bv;
nf->bv_off = f->bv_off;
nf->waited = 0;
+ nf->sent_jiffs = f->sent_jiffs;
f->skb = skb;
aoe_freetframe(f);
ht->nout--;
@@ -621,7 +658,7 @@ rexmit_timer(ulong vp)
head = &d->factive[i];
list_for_each_safe(pos, nx, head) {
f = list_entry(pos, struct frame, head);
- if (tsince(f->tag) < timeout)
+ if (tsince_hr(f) < timeout)
break; /* end of expired frames */
/* move to flist for later processing */
list_move_tail(pos, &flist);
@@ -632,8 +669,8 @@ rexmit_timer(ulong vp)
while (!list_empty(&flist)) {
pos = flist.next;
f = list_entry(pos, struct frame, head);
- n = f->waited += tsince(f->tag);
- n /= HZ;
+ n = f->waited += tsince_hr(f);
+ n /= USEC_PER_SEC;
if (n > aoe_deadsecs) {
/* Waited too long. Device failure.
* Hang all frames on first hash bucket for downdev
@@ -1193,12 +1230,12 @@ aoecmd_ata_rsp(struct sk_buff *skb)
n = be32_to_cpu(get_unaligned(&h->tag));
f = getframe(d, n);
if (f) {
- calc_rttavg(d, f->t, tsince(n));
+ calc_rttavg(d, f->t, tsince_hr(f));
f->t->nout--;
} else {
f = getframe_deferred(d, n);
if (f) {
- calc_rttavg(d, NULL, tsince(n));
+ calc_rttavg(d, NULL, tsince_hr(f));
} else {
calc_rttavg(d, NULL, tsince(n));
spin_unlock_irqrestore(&d->lock, flags);
@@ -1276,7 +1313,13 @@ aoecmd_ata_id(struct aoedev *d)
d->rttdev = RTTDEV_INIT;
d->timer.function = rexmit_timer;
- return skb_clone(skb, GFP_ATOMIC);
+ skb = skb_clone(skb, GFP_ATOMIC);
+ if (skb) {
+ do_gettimeofday(&f->sent);
+ f->sent_jiffs = (u32) jiffies;
+ }
+
+ return skb;
}
static struct aoetgt *
--
1.7.1
--
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