On Thu, 15 May 2014 09:50:49 +0200 Patrik Horník <patrik@xxxxxx> wrote:
> OK, it seems that because of that my copy operations will not be
> finished yet by next week... :)
>
> BTW this time layout is left-symetric but the problem I guess is in
> whole strip' write detection with degraded RAID6.
>
> Patrik
>
> 2014-05-15 9:18 GMT+02:00 NeilBrown <neilb@xxxxxxx>:
> > On Thu, 15 May 2014 09:04:27 +0200 Patrik Horník <patrik@xxxxxx> wrote:
> >
> >> Hello Neil,
> >>
> >> did you make some progress on this issue by any chance?
> >
> > No I haven't - sorry.
> > After 2 year, I guess I really should.
> >
> > I'll make another note for first thing next week.
Can you try the following patch and let me know if it helps?
I definitely reduced the number of reads significantly, but my measurements
(of a very simple test case) didn't show much speed-up.
This is against current mainline. If you want it against another version and
it doesn't apply easily, just ask.
Thanks,
NeilBrown
From 98c411f93391be0dbda98d43835dd9e042faa78f Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@xxxxxxx>
Date: Mon, 19 May 2014 11:16:49 +1000
Subject: [PATCH] md/raid56: Don't perform reads to support writes until stripe
is ready.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
If it is found that we need to pre-read some blocks before a write
can succeed, we normally set STRIPE_DELAYED and don't actually perform
the read until STRIPE_PREREAD_ACTIVE subsequently gets set.
However for a degraded RAID6 we currently perform the reads as soon
as we see that a write is pending. This significantly hurts
throughput.
So:
- when handle_stripe_dirtying find a block that it wants on a device
that is failed, set STRIPE_DELAY, instead of doing nothing, and
- when fetch_block detects that a read might be required to satisfy a
write, only perform the read if STRIPE_PREREAD_ACTIVE is set,
and if we would actually need to read something to complete the write.
This also helps RAID5, though less often as RAID5 supports a
read-modify-write cycle. For RAID5 the read is performed too early
only if the write is not a full 4K aligned write (i.e. no an
R5_OVERWRITE).
Also clean up a couple of horrible bits of formatting.
Reported-by: Patrik Horník <patrik@xxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 633e20a96b34..d67202bd9118 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -292,9 +292,12 @@ static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh,
BUG_ON(atomic_read(&conf->active_stripes)==0);
if (test_bit(STRIPE_HANDLE, &sh->state)) {
if (test_bit(STRIPE_DELAYED, &sh->state) &&
- !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+ !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
list_add_tail(&sh->lru, &conf->delayed_list);
- else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
+ if (atomic_read(&conf->preread_active_stripes)
+ < IO_THRESHOLD)
+ md_wakeup_thread(conf->mddev->thread);
+ } else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
sh->bm_seq - conf->seq_write > 0)
list_add_tail(&sh->lru, &conf->bitmap_list);
else {
@@ -2908,8 +2911,11 @@ static int fetch_block(struct stripe_head *sh, struct stripe_head_state *s,
(s->failed >= 1 && fdev[0]->toread) ||
(s->failed >= 2 && fdev[1]->toread) ||
(sh->raid_conf->level <= 5 && s->failed && fdev[0]->towrite &&
+ (!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) &&
!test_bit(R5_OVERWRITE, &fdev[0]->flags)) ||
- (sh->raid_conf->level == 6 && s->failed && s->to_write))) {
+ (sh->raid_conf->level == 6 && s->failed && s->to_write &&
+ s->towrite < sh->raid_conf->raid_disks - 2 &&
+ (!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))))) {
/* we would like to get this block, possibly by computing it,
* otherwise read it if the backing disk is insync
*/
@@ -3115,7 +3121,8 @@ static void handle_stripe_dirtying(struct r5conf *conf,
!test_bit(R5_LOCKED, &dev->flags) &&
!(test_bit(R5_UPTODATE, &dev->flags) ||
test_bit(R5_Wantcompute, &dev->flags))) {
- if (test_bit(R5_Insync, &dev->flags)) rcw++;
+ if (test_bit(R5_Insync, &dev->flags))
+ rcw++;
else
rcw += 2*disks;
}
@@ -3136,10 +3143,10 @@ static void handle_stripe_dirtying(struct r5conf *conf,
!(test_bit(R5_UPTODATE, &dev->flags) ||
test_bit(R5_Wantcompute, &dev->flags)) &&
test_bit(R5_Insync, &dev->flags)) {
- if (
- test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
- pr_debug("Read_old block "
- "%d for r-m-w\n", i);
+ if (test_bit(STRIPE_PREREAD_ACTIVE,
+ &sh->state)) {
+ pr_debug("Read_old block %d for r-m-w\n",
+ i);
set_bit(R5_LOCKED, &dev->flags);
set_bit(R5_Wantread, &dev->flags);
s->locked++;
@@ -3162,10 +3169,9 @@ static void handle_stripe_dirtying(struct r5conf *conf,
!(test_bit(R5_UPTODATE, &dev->flags) ||
test_bit(R5_Wantcompute, &dev->flags))) {
rcw++;
- if (!test_bit(R5_Insync, &dev->flags))
- continue; /* it's a failed drive */
- if (
- test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
+ if (test_bit(R5_Insync, &dev->flags) &&
+ test_bit(STRIPE_PREREAD_ACTIVE,
+ &sh->state)) {
pr_debug("Read_old block "
"%d for Reconstruct\n", i);
set_bit(R5_LOCKED, &dev->flags);
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