Commit 5f0c9c48 authored by Ed Cashin's avatar Ed Cashin Committed by Linus Torvalds
Browse files

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: default avatarEd Cashin <ecashin@coraid.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0d555ecf

drivers/block/aoe/aoe.h

+5 −4
Original line number Diff line number Diff line
@@ -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;

drivers/block/aoe/aoecmd.c

+50 −7
Original line number Diff line number Diff line
@@ -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);
@@ -475,11 +477,45 @@ 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)

{
@@ -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 *

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