[md-accel PATCH 09/19] md: handle_stripe5 - add request/completion logic for async write ops

Dan Williams
2007-06-27T01:54:56Z

After handle_stripe5 decides whether it wants to perform a
read-modify-write, or a reconstruct write it calls
handle_write_operations5. A read-modify-write operation will perform an
xor subtraction of the blocks marked with the R5_Wantprexor flag, copy the
new data into the stripe (biodrain) and perform a postxor operation across
all up-to-date blocks to generate the new parity. A reconstruct write is run
when all blocks are already up-to-date in the cache so all that is needed
is a biodrain and postxor.

On the completion path STRIPE_OP_PREXOR will be set if the operation was a
read-modify-write. The STRIPE_OP_BIODRAIN flag is used in the completion
path to differentiate write-initiated postxor operations versus
expansion-initiated postxor operations. Completion of a write triggers i/o
to the drives.

Changelog:
* make the 'rcw' parameter to handle_write_operations5 a simple flag, Neil Brown
* remove test_and_set/test_and_clear BUG_ONs, Neil Brown

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-By: NeilBrown <neilb@suse.de>
---

drivers/md/raid5.c | 161 +++++++++++++++++++++++++++++++++++++++++++++-------
1 files changed, 138 insertions(+), 23 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 7c688f6..b2e88fe 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1815,7 +1815,79 @@ static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
}
}

+static int
+handle_write_operations5(struct stripe_head *sh, int rcw, int expand)
+{
+ int i, pd_idx = sh->pd_idx, disks = sh->disks;
+ int locked = 0;
+
+ if (rcw) {
+ /* if we are not expanding this is a proper write request, and
+ * there will be bios with new data to be drained into the
+ * stripe cache
+ */
+ if (!expand) {
+ set_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);
+ sh->ops.count++;
+ }
+
+ set_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);
+ sh->ops.count++;
+
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+
+ if (dev->towrite) {
+ set_bit(R5_LOCKED, &dev->flags);
+ if (!expand)
+ clear_bit(R5_UPTODATE, &dev->flags);
+ locked++;
+ }
+ }
+ } else {
+ BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||
+ test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));
+
+ set_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
+ set_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);
+ set_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);
+
+ sh->ops.count += 3;
+
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ if (i == pd_idx)
+ continue;
+
+ /* For a read-modify write there may be blocks that are
+ * locked for reading while others are ready to be
+ * written so we distinguish these blocks by the
+ * R5_Wantprexor bit
+ */
+ if (dev->towrite &&
+ (test_bit(R5_UPTODATE, &dev->flags) ||
+ test_bit(R5_Wantcompute, &dev->flags))) {
+ set_bit(R5_Wantprexor, &dev->flags);
+ set_bit(R5_LOCKED, &dev->flags);
+ clear_bit(R5_UPTODATE, &dev->flags);
+ locked++;
+ }
+ }
+ }
+
+ /* keep the parity disk locked while asynchronous operations
+ * are in flight
+ */
+ set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);
+ clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+ locked++;

+ pr_debug("%s: stripe %llu locked: %d pending: %lx\n",
+ __FUNCTION__, (unsigned long long)sh->sector,
+ locked, sh->ops.pending);
+
+ return locked;
+}

/*
* Each stripe/dev can have one or more bion attached.
@@ -2210,27 +2282,8 @@ static void handle_issuing_new_write_requests5(raid5_conf_t *conf,
* we can start a write request
*/
if (s->locked == 0 && (rcw == 0 || rmw == 0) &&
- !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
- pr_debug("Computing parity...\n");
- compute_parity5(sh, rcw == 0 ?
- RECONSTRUCT_WRITE : READ_MODIFY_WRITE);
- /* now every locked buffer is ready to be written */
- for (i = disks; i--; )
- if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
- pr_debug("Writing block %d\n", i);
- s->locked++;
- set_bit(R5_Wantwrite, &sh->dev[i].flags);
- if (!test_bit(R5_Insync, &sh->dev[i].flags)
- || (i == sh->pd_idx && s->failed == 0))
- set_bit(STRIPE_INSYNC, &sh->state);
- }
- if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
- atomic_dec(&conf->preread_active_stripes);
- if (atomic_read(&conf->preread_active_stripes) <
- IO_THRESHOLD)
- md_wakeup_thread(conf->mddev->thread);
- }
- }
+ !test_bit(STRIPE_BIT_DELAY, &sh->state))
+ s->locked += handle_write_operations5(sh, rcw == 0, 0);
}

static void handle_issuing_new_write_requests6(raid5_conf_t *conf,
@@ -2649,8 +2702,70 @@ static void handle_stripe5(struct stripe_head *sh)
(s.syncing && (s.uptodate < disks)) || s.expanding)
handle_issuing_new_read_requests5(sh, &s, disks);

- /* now to consider writing and what else, if anything should be read */
- if (s.to_write)
+ /* Now we check to see if any write operations have recently
+ * completed
+ */
+
+ /* leave prexor set until postxor is done, allows us to distinguish
+ * a rmw from a rcw during biodrain
+ */
+ if (test_bit(STRIPE_OP_PREXOR, &sh->ops.complete) &&
+ test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete)) {
+
+ clear_bit(STRIPE_OP_PREXOR, &sh->ops.complete);
+ clear_bit(STRIPE_OP_PREXOR, &sh->ops.ack);
+ clear_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
+
+ for (i = disks; i--; )
+ clear_bit(R5_Wantprexor, &sh->dev[i].flags);
+ }
+
+ /* if only POSTXOR is set then this is an 'expand' postxor */
+ if (test_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete) &&
+ test_bit(STRIPE_OP_POSTXOR, &sh->ops.complete)) {
+
+ clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete);
+ clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.ack);
+ clear_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending);
+
+ clear_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);
+ clear_bit(STRIPE_OP_POSTXOR, &sh->ops.ack);
+ clear_bit(STRIPE_OP_POSTXOR, &sh->ops.pending);
+
+ /* All the 'written' buffers and the parity block are ready to
+ * be written back to disk
+ */
+ BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags));
+ for (i = disks; i--; ) {
+ dev = &sh->dev[i];
+ if (test_bit(R5_LOCKED, &dev->flags) &&
+ (i == sh->pd_idx || dev->written)) {
+ pr_debug("Writing block %d\n", i);
+ set_bit(R5_Wantwrite, &dev->flags);
+ if (!test_and_set_bit(
+ STRIPE_OP_IO, &sh->ops.pending))
+ sh->ops.count++;
+ if (!test_bit(R5_Insync, &dev->flags) ||
+ (i == sh->pd_idx && s.failed == 0))
+ set_bit(STRIPE_INSYNC, &sh->state);
+ }
+ }
+ if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
+ atomic_dec(&conf->preread_active_stripes);
+ if (atomic_read(&conf->preread_active_stripes) <
+ IO_THRESHOLD)
+ md_wakeup_thread(conf->mddev->thread);
+ }
+ }
+
+ /* Now to consider new write requests and what else, if anything
+ * should be read. We do not handle new writes when:
+ * 1/ A 'write' operation (copy+xor) is already in flight.
+ * 2/ A 'check' operation is in flight, as it may clobber the parity
+ * block.
+ */
+ if (s.to_write && !test_bit(STRIPE_OP_POSTXOR, &sh->ops.pending) &&
+ !test_bit(STRIPE_OP_CHECK, &sh->ops.pending))
handle_issuing_new_write_requests5(conf, sh, &s, disks);

/* maybe we need to check and possibly fix the parity for this stripe