[md-accel PATCH 07/19] md: raid5_run_ops - run stripe operations outside sh->lock

Dan Williams
2007-06-27T01:54:21Z

When the raid acceleration work was proposed, Neil laid out the following
attack plan:

1/ move the xor and copy operations outside spin_lock(&sh->lock)
2/ find/implement an asynchronous offload api

The raid5_run_ops routine uses the asynchronous offload api (async_tx) and
the stripe_operations member of a stripe_head to carry out xor+copy
operations asynchronously, outside the lock.

To perform operations outside the lock a new set of state flags is needed
to track new requests, in-flight requests, and completed requests. In this
new model handle_stripe is tasked with scanning the stripe_head for work,
updating the stripe_operations structure, and finally dropping the lock and
calling raid5_run_ops for processing. The following flags outline the
requests that handle_stripe can make of raid5_run_ops:

STRIPE_OP_BIOFILL
- copy data into request buffers to satisfy a read request
STRIPE_OP_COMPUTE_BLK
- generate a missing block in the cache from the other blocks
STRIPE_OP_PREXOR
- subtract existing data as part of the read-modify-write process
STRIPE_OP_BIODRAIN
- copy data out of request buffers to satisfy a write request
STRIPE_OP_POSTXOR
- recalculate parity for new data that has entered the cache
STRIPE_OP_CHECK
- verify that the parity is correct
STRIPE_OP_IO
- submit i/o to the member disks (note this was already performed outside
the stripe lock, but it made sense to add it as an operation type

The flow is:
1/ handle_stripe sets STRIPE_OP_* in sh->ops.pending
2/ raid5_run_ops reads sh->ops.pending, sets sh->ops.ack, and submits the
operation to the async_tx api
3/ async_tx triggers the completion callback routine to set
sh->ops.complete and release the stripe
4/ handle_stripe runs again to finish the operation and optionally submit
new operations that were previously blocked

Note this patch just defines raid5_run_ops, subsequent commits (one per
major operation type) modify handle_stripe to take advantage of this
routine.

Changelog:
* removed ops_complete_biodrain in favor of ops_complete_postxor and
ops_complete_write.
* removed the raid5_run_ops workqueue
* call bi_end_io for reads in ops_complete_biofill, saves a call to
handle_stripe
* explicitly handle the 2-disk raid5 case (xor becomes memcpy), Neil Brown
* fix race between async engines and bi_end_io call for reads, Neil Brown
* remove unnecessary spin_lock from ops_complete_biofill
* remove test_and_set/test_and_clear BUG_ONs, Neil Brown
* remove explicit interrupt handling for channel switching, this feature
was absorbed (i.e. it is now implicit) by the async_tx api

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

drivers/md/raid5.c | 546 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/raid/raid5.h | 81 ++++++-
2 files changed, 624 insertions(+), 3 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index d21fa7a..34fcda0 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -52,6 +52,7 @@
#include "raid6.h"

#include <linux/raid/bitmap.h>
+#include <linux/async_tx.h>

/*
* Stripe cache
@@ -324,6 +325,551 @@ static struct stripe_head *get_active_stripe(raid5_conf_t *conf, sector_t sector
return sh;
}

+static int
+raid5_end_read_request(struct bio *bi, unsigned int bytes_done, int error);
+static int
+raid5_end_write_request (struct bio *bi, unsigned int bytes_done, int error);
+
+static void ops_run_io(struct stripe_head *sh)
+{
+ raid5_conf_t *conf = sh->raid_conf;
+ int i, disks = sh->disks;
+
+ might_sleep();
+
+ for (i = disks; i--; ) {
+ int rw;
+ struct bio *bi;
+ mdk_rdev_t *rdev;
+ if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
+ rw = WRITE;
+ else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
+ rw = READ;
+ else
+ continue;
+
+ bi = &sh->dev[i].req;
+
+ bi->bi_rw = rw;
+ if (rw == WRITE)
+ bi->bi_end_io = raid5_end_write_request;
+ else
+ bi->bi_end_io = raid5_end_read_request;
+
+ rcu_read_lock();
+ rdev = rcu_dereference(conf->disks[i].rdev);
+ if (rdev && test_bit(Faulty, &rdev->flags))
+ rdev = NULL;
+ if (rdev)
+ atomic_inc(&rdev->nr_pending);
+ rcu_read_unlock();
+
+ if (rdev) {
+ if (test_bit(STRIPE_SYNCING, &sh->state) ||
+ test_bit(STRIPE_EXPAND_SOURCE, &sh->state) ||
+ test_bit(STRIPE_EXPAND_READY, &sh->state))
+ md_sync_acct(rdev->bdev, STRIPE_SECTORS);
+
+ bi->bi_bdev = rdev->bdev;
+ pr_debug("%s: for %llu schedule op %ld on disc %d\n",
+ __FUNCTION__, (unsigned long long)sh->sector,
+ bi->bi_rw, i);
+ atomic_inc(&sh->count);
+ bi->bi_sector = sh->sector + rdev->data_offset;
+ bi->bi_flags = 1 << BIO_UPTODATE;
+ bi->bi_vcnt = 1;
+ bi->bi_max_vecs = 1;
+ bi->bi_idx = 0;
+ bi->bi_io_vec = &sh->dev[i].vec;
+ bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
+ bi->bi_io_vec[0].bv_offset = 0;
+ bi->bi_size = STRIPE_SIZE;
+ bi->bi_next = NULL;
+ if (rw == WRITE &&
+ test_bit(R5_ReWrite, &sh->dev[i].flags))
+ atomic_add(STRIPE_SECTORS,
+ &rdev->corrected_errors);
+ generic_make_request(bi);
+ } else {
+ if (rw == WRITE)
+ set_bit(STRIPE_DEGRADED, &sh->state);
+ pr_debug("skip op %ld on disc %d for sector %llu\n",
+ bi->bi_rw, i, (unsigned long long)sh->sector);
+ clear_bit(R5_LOCKED, &sh->dev[i].flags);
+ set_bit(STRIPE_HANDLE, &sh->state);
+ }
+ }
+}
+
+static struct dma_async_tx_descriptor *
+async_copy_data(int frombio, struct bio *bio, struct page *page,
+ sector_t sector, struct dma_async_tx_descriptor *tx)
+{
+ struct bio_vec *bvl;
+ struct page *bio_page;
+ int i;
+ int page_offset;
+
+ if (bio->bi_sector >= sector)
+ page_offset = (signed)(bio->bi_sector - sector) * 512;
+ else
+ page_offset = (signed)(sector - bio->bi_sector) * -512;
+ bio_for_each_segment(bvl, bio, i) {
+ int len = bio_iovec_idx(bio, i)->bv_len;
+ int clen;
+ int b_offset = 0;
+
+ if (page_offset < 0) {
+ b_offset = -page_offset;
+ page_offset += b_offset;
+ len -= b_offset;
+ }
+
+ if (len > 0 && page_offset + len > STRIPE_SIZE)
+ clen = STRIPE_SIZE - page_offset;
+ else
+ clen = len;
+
+ if (clen > 0) {
+ b_offset += bio_iovec_idx(bio, i)->bv_offset;
+ bio_page = bio_iovec_idx(bio, i)->bv_page;
+ if (frombio)
+ tx = async_memcpy(page, bio_page, page_offset,
+ b_offset, clen,
+ ASYNC_TX_DEP_ACK | ASYNC_TX_KMAP_SRC,
+ tx, NULL, NULL);
+ else
+ tx = async_memcpy(bio_page, page, b_offset,
+ page_offset, clen,
+ ASYNC_TX_DEP_ACK | ASYNC_TX_KMAP_DST,
+ tx, NULL, NULL);
+ }
+ if (clen < len) /* hit end of page */
+ break;
+ page_offset += len;
+ }
+
+ return tx;
+}
+
+static void ops_complete_biofill(void *stripe_head_ref)
+{
+ struct stripe_head *sh = stripe_head_ref;
+ struct bio *return_bi = NULL, *bi;
+ raid5_conf_t *conf = sh->raid_conf;
+ int i, more_to_read = 0;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ /* clear completed biofills */
+ for (i = sh->disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ /* check if this stripe has new incoming reads */
+ if (dev->toread)
+ more_to_read++;
+
+ /* acknowledge completion of a biofill operation */
+ /* and check if we need to reply to a read request
+ */
+ if (test_bit(R5_Wantfill, &dev->flags) && !dev->toread) {
+ struct bio *rbi, *rbi2;
+ clear_bit(R5_Wantfill, &dev->flags);
+
+ /* The access to dev->read is outside of the
+ * spin_lock_irq(&conf->device_lock), but is protected
+ * by the STRIPE_OP_BIOFILL pending bit
+ */
+ BUG_ON(!dev->read);
+ rbi = dev->read;
+ dev->read = NULL;
+ while (rbi && rbi->bi_sector <
+ dev->sector + STRIPE_SECTORS) {
+ rbi2 = r5_next_bio(rbi, dev->sector);
+ spin_lock_irq(&conf->device_lock);
+ if (--rbi->bi_phys_segments == 0) {
+ rbi->bi_next = return_bi;
+ return_bi = rbi;
+ }
+ spin_unlock_irq(&conf->device_lock);
+ rbi = rbi2;
+ }
+ }
+ }
+ clear_bit(STRIPE_OP_BIOFILL, &sh->ops.ack);
+ clear_bit(STRIPE_OP_BIOFILL, &sh->ops.pending);
+
+ bi = return_bi;
+ while (bi) {
+ int bytes = bi->bi_size;
+
+ return_bi = bi->bi_next;
+ bi->bi_next = NULL;
+ bi->bi_size = 0;
+ bi->bi_end_io(bi, bytes,
+ test_bit(BIO_UPTODATE, &bi->bi_flags) ? 0 : -EIO);
+ bi = return_bi;
+ }
+
+ if (more_to_read)
+ set_bit(STRIPE_HANDLE, &sh->state);
+ release_stripe(sh);
+}
+
+static void ops_run_biofill(struct stripe_head *sh)
+{
+ struct dma_async_tx_descriptor *tx = NULL;
+ raid5_conf_t *conf = sh->raid_conf;
+ int i;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ for (i = sh->disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ if (test_bit(R5_Wantfill, &dev->flags)) {
+ struct bio *rbi;
+ spin_lock_irq(&conf->device_lock);
+ dev->read = rbi = dev->toread;
+ dev->toread = NULL;
+ spin_unlock_irq(&conf->device_lock);
+ while (rbi && rbi->bi_sector <
+ dev->sector + STRIPE_SECTORS) {
+ tx = async_copy_data(0, rbi, dev->page,
+ dev->sector, tx);
+ rbi = r5_next_bio(rbi, dev->sector);
+ }
+ }
+ }
+
+ atomic_inc(&sh->count);
+ async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
+ ops_complete_biofill, sh);
+}
+
+static void ops_complete_compute5(void *stripe_head_ref)
+{
+ struct stripe_head *sh = stripe_head_ref;
+ int target = sh->ops.target;
+ struct r5dev *tgt = &sh->dev[target];
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ set_bit(R5_UPTODATE, &tgt->flags);
+ BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
+ clear_bit(R5_Wantcompute, &tgt->flags);
+ set_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.complete);
+ set_bit(STRIPE_HANDLE, &sh->state);
+ release_stripe(sh);
+}
+
+static struct dma_async_tx_descriptor *
+ops_run_compute5(struct stripe_head *sh, unsigned long pending)
+{
+ /* kernel stack size limits the total number of disks */
+ int disks = sh->disks;
+ struct page *xor_srcs[disks];
+ int target = sh->ops.target;
+ struct r5dev *tgt = &sh->dev[target];
+ struct page *xor_dest = tgt->page;
+ int count = 0;
+ struct dma_async_tx_descriptor *tx;
+ int i;
+
+ pr_debug("%s: stripe %llu block: %d\n",
+ __FUNCTION__, (unsigned long long)sh->sector, target);
+ BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
+
+ for (i = disks; i--; )
+ if (i != target)
+ xor_srcs[count++] = sh->dev[i].page;
+
+ atomic_inc(&sh->count);
+
+ if (unlikely(count == 1))
+ tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE,
+ 0, NULL, ops_complete_compute5, sh);
+ else
+ tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
+ ASYNC_TX_XOR_ZERO_DST, NULL,
+ ops_complete_compute5, sh);
+
+ /* ack now if postxor is not set to be run */
+ if (tx && !test_bit(STRIPE_OP_POSTXOR, &pending))
+ async_tx_ack(tx);
+
+ return tx;
+}
+
+static void ops_complete_prexor(void *stripe_head_ref)
+{
+ struct stripe_head *sh = stripe_head_ref;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ set_bit(STRIPE_OP_PREXOR, &sh->ops.complete);
+}
+
+static struct dma_async_tx_descriptor *
+ops_run_prexor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
+{
+ /* kernel stack size limits the total number of disks */
+ int disks = sh->disks;
+ struct page *xor_srcs[disks];
+ int count = 0, pd_idx = sh->pd_idx, i;
+
+ /* existing parity data subtracted */
+ struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ /* Only process blocks that are known to be uptodate */
+ if (dev->towrite && test_bit(R5_Wantprexor, &dev->flags))
+ xor_srcs[count++] = dev->page;
+ }
+
+ tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
+ ASYNC_TX_DEP_ACK | ASYNC_TX_XOR_DROP_DST, tx,
+ ops_complete_prexor, sh);
+
+ return tx;
+}
+
+static struct dma_async_tx_descriptor *
+ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
+{
+ int disks = sh->disks;
+ int pd_idx = sh->pd_idx, i;
+
+ /* check if prexor is active which means only process blocks
+ * that are part of a read-modify-write (Wantprexor)
+ */
+ int prexor = test_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ struct bio *chosen;
+ int towrite;
+
+ towrite = 0;
+ if (prexor) { /* rmw */
+ if (dev->towrite &&
+ test_bit(R5_Wantprexor, &dev->flags))
+ towrite = 1;
+ } else { /* rcw */
+ if (i != pd_idx && dev->towrite &&
+ test_bit(R5_LOCKED, &dev->flags))
+ towrite = 1;
+ }
+
+ if (towrite) {
+ struct bio *wbi;
+
+ spin_lock(&sh->lock);
+ chosen = dev->towrite;
+ dev->towrite = NULL;
+ BUG_ON(dev->written);
+ wbi = dev->written = chosen;
+ spin_unlock(&sh->lock);
+
+ while (wbi && wbi->bi_sector <
+ dev->sector + STRIPE_SECTORS) {
+ tx = async_copy_data(1, wbi, dev->page,
+ dev->sector, tx);
+ wbi = r5_next_bio(wbi, dev->sector);
+ }
+ }
+ }
+
+ return tx;
+}
+
+static void ops_complete_postxor(void *stripe_head_ref)
+{
+ struct stripe_head *sh = stripe_head_ref;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ set_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);
+ set_bit(STRIPE_HANDLE, &sh->state);
+ release_stripe(sh);
+}
+
+static void ops_complete_write(void *stripe_head_ref)
+{
+ struct stripe_head *sh = stripe_head_ref;
+ int disks = sh->disks, i, pd_idx = sh->pd_idx;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ if (dev->written || i == pd_idx)
+ set_bit(R5_UPTODATE, &dev->flags);
+ }
+
+ set_bit(STRIPE_OP_BIODRAIN, &sh->ops.complete);
+ set_bit(STRIPE_OP_POSTXOR, &sh->ops.complete);
+
+ set_bit(STRIPE_HANDLE, &sh->state);
+ release_stripe(sh);
+}
+
+static void
+ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
+{
+ /* kernel stack size limits the total number of disks */
+ int disks = sh->disks;
+ struct page *xor_srcs[disks];
+
+ int count = 0, pd_idx = sh->pd_idx, i;
+ struct page *xor_dest;
+ int prexor = test_bit(STRIPE_OP_PREXOR, &sh->ops.pending);
+ unsigned long flags;
+ dma_async_tx_callback callback;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ /* check if prexor is active which means only process blocks
+ * that are part of a read-modify-write (written)
+ */
+ if (prexor) {
+ xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ if (dev->written)
+ xor_srcs[count++] = dev->page;
+ }
+ } else {
+ xor_dest = sh->dev[pd_idx].page;
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ if (i != pd_idx)
+ xor_srcs[count++] = dev->page;
+ }
+ }
+
+ /* check whether this postxor is part of a write */
+ callback = test_bit(STRIPE_OP_BIODRAIN, &sh->ops.pending) ?
+ ops_complete_write : ops_complete_postxor;
+
+ /* 1/ if we prexor'd then the dest is reused as a source
+ * 2/ if we did not prexor then we are redoing the parity
+ * set ASYNC_TX_XOR_DROP_DST and ASYNC_TX_XOR_ZERO_DST
+ * for the synchronous xor case
+ */
+ flags = ASYNC_TX_DEP_ACK | ASYNC_TX_ACK |
+ (prexor ? ASYNC_TX_XOR_DROP_DST : ASYNC_TX_XOR_ZERO_DST);
+
+ atomic_inc(&sh->count);
+
+ if (unlikely(count == 1)) {
+ flags &= ~(ASYNC_TX_XOR_DROP_DST | ASYNC_TX_XOR_ZERO_DST);
+ tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE,
+ flags, tx, callback, sh);
+ } else
+ tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
+ flags, tx, callback, sh);
+}
+
+static void ops_complete_check(void *stripe_head_ref)
+{
+ struct stripe_head *sh = stripe_head_ref;
+ int pd_idx = sh->pd_idx;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ if (test_and_clear_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending) &&
+ sh->ops.zero_sum_result == 0)
+ set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+
+ set_bit(STRIPE_OP_CHECK, &sh->ops.complete);
+ set_bit(STRIPE_HANDLE, &sh->state);
+ release_stripe(sh);
+}
+
+static void ops_run_check(struct stripe_head *sh)
+{
+ /* kernel stack size limits the total number of disks */
+ int disks = sh->disks;
+ struct page *xor_srcs[disks];
+ struct dma_async_tx_descriptor *tx;
+
+ int count = 0, pd_idx = sh->pd_idx, i;
+ struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
+
+ pr_debug("%s: stripe %llu\n", __FUNCTION__,
+ (unsigned long long)sh->sector);
+
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ if (i != pd_idx)
+ xor_srcs[count++] = dev->page;
+ }
+
+ tx = async_xor_zero_sum(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
+ &sh->ops.zero_sum_result, 0, NULL, NULL, NULL);
+
+ if (tx)
+ set_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending);
+ else
+ clear_bit(STRIPE_OP_MOD_DMA_CHECK, &sh->ops.pending);
+
+ atomic_inc(&sh->count);
+ tx = async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
+ ops_complete_check, sh);
+}
+
+static void raid5_run_ops(struct stripe_head *sh, unsigned long pending)
+{
+ int overlap_clear = 0, i, disks = sh->disks;
+ struct dma_async_tx_descriptor *tx = NULL;
+
+ if (test_bit(STRIPE_OP_BIOFILL, &pending)) {
+ ops_run_biofill(sh);
+ overlap_clear++;
+ }
+
+ if (test_bit(STRIPE_OP_COMPUTE_BLK, &pending))
+ tx = ops_run_compute5(sh, pending);
+
+ if (test_bit(STRIPE_OP_PREXOR, &pending))
+ tx = ops_run_prexor(sh, tx);
+
+ if (test_bit(STRIPE_OP_BIODRAIN, &pending)) {
+ tx = ops_run_biodrain(sh, tx);
+ overlap_clear++;
+ }
+
+ if (test_bit(STRIPE_OP_POSTXOR, &pending))
+ ops_run_postxor(sh, tx);
+
+ if (test_bit(STRIPE_OP_CHECK, &pending))
+ ops_run_check(sh);
+
+ if (test_bit(STRIPE_OP_IO, &pending))
+ ops_run_io(sh);
+
+ if (overlap_clear)
+ for (i = disks; i--; ) {
+ struct r5dev *dev = &sh->dev[i];
+ if (test_and_clear_bit(R5_Overlap, &dev->flags))
+ wake_up(&sh->raid_conf->wait_for_overlap);
+ }
+}
+
static int grow_one_stripe(raid5_conf_t *conf)
{
struct stripe_head *sh;
diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index 208aa68..f623a44 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -116,13 +116,46 @@
* attach a request to an active stripe (add_stripe_bh())
* lockdev attach-buffer unlockdev
* handle a stripe (handle_stripe())
- * lockstripe clrSTRIPE_HANDLE ... (lockdev check-buffers unlockdev) .. change-state .. record io needed unlockstripe schedule io
+ * lockstripe clrSTRIPE_HANDLE ...
+ * (lockdev check-buffers unlockdev) ..
+ * change-state ..
+ * record io/ops needed unlockstripe schedule io/ops
* release an active stripe (release_stripe())
* lockdev if (!--cnt) { if STRIPE_HANDLE, add to handle_list else add to inactive-list } unlockdev
*
* The refcount counts each thread that have activated the stripe,
* plus raid5d if it is handling it, plus one for each active request
- * on a cached buffer.
+ * on a cached buffer, and plus one if the stripe is undergoing stripe
+ * operations.
+ *
+ * Stripe operations are performed outside the stripe lock,
+ * the stripe operations are:
+ * -copying data between the stripe cache and user application buffers
+ * -computing blocks to save a disk access, or to recover a missing block
+ * -updating the parity on a write operation (reconstruct write and
+ * read-modify-write)
+ * -checking parity correctness
+ * -running i/o to disk
+ * These operations are carried out by raid5_run_ops which uses the async_tx
+ * api to (optionally) offload operations to dedicated hardware engines.
+ * When requesting an operation handle_stripe sets the pending bit for the
+ * operation and increments the count. raid5_run_ops is then run whenever
+ * the count is non-zero.
+ * There are some critical dependencies between the operations that prevent some
+ * from being requested while another is in flight.
+ * 1/ Parity check operations destroy the in cache version of the parity block,
+ * so we prevent parity dependent operations like writes and compute_blocks
+ * from starting while a check is in progress. Some dma engines can perform
+ * the check without damaging the parity block, in these cases the parity
+ * block is re-marked up to date (assuming the check was successful) and is
+ * not re-read from disk.
+ * 2/ When a write operation is requested we immediately lock the affected
+ * blocks, and mark them as not up to date. This causes new read requests
+ * to be held off, as well as parity checks and compute block operations.
+ * 3/ Once a compute block operation has been requested handle_stripe treats
+ * that block as if it is up to date. raid5_run_ops guaruntees that any
+ * operation that is dependent on the compute block result is initiated after
+ * the compute block completes.
*/

struct stripe_head {
@@ -136,11 +169,26 @@ struct stripe_head {
spinlock_t lock;
int bm_seq; /* sequence number for bitmap flushes */
int disks; /* disks in stripe */
+ /* stripe_operations
+ * @pending - pending ops flags (set for request->issue->complete)
+ * @ack - submitted ops flags (set for issue->complete)
+ * @complete - completed ops flags (set for complete)
+ * @target - STRIPE_OP_COMPUTE_BLK target
+ * @count - raid5_runs_ops is set to run when this is non-zero
+ */
+ struct stripe_operations {
+ unsigned long pending;
+ unsigned long ack;
+ unsigned long complete;
+ int target;
+ int count;
+ u32 zero_sum_result;
+ } ops;
struct r5dev {
struct bio req;
struct bio_vec vec;
struct page *page;
- struct bio *toread, *towrite, *written;
+ struct bio *toread, *read, *towrite, *written;
sector_t sector; /* sector of this page */
unsigned long flags;
} dev[1]; /* allocated with extra space depending of RAID geometry */
@@ -174,6 +222,15 @@ struct r6_state {
#define R5_ReWrite 9 /* have tried to over-write the readerror */

#define R5_Expanded 10 /* This block now has post-expand data */
+#define R5_Wantcompute 11 /* compute_block in progress treat as
+ * uptodate
+ */
+#define R5_Wantfill 12 /* dev->toread contains a bio that needs
+ * filling
+ */
+#define R5_Wantprexor 13 /* distinguish blocks ready for rmw from
+ * other "towrites"
+ */
/*
* Write method
*/
@@ -196,6 +253,24 @@ struct r6_state {
#define STRIPE_EXPAND_SOURCE 10
#define STRIPE_EXPAND_READY 11
/*
+ * Operations flags (in issue order)
+ */
+#define STRIPE_OP_BIOFILL 0
+#define STRIPE_OP_COMPUTE_BLK 1
+#define STRIPE_OP_PREXOR 2
+#define STRIPE_OP_BIODRAIN 3
+#define STRIPE_OP_POSTXOR 4
+#define STRIPE_OP_CHECK 5
+#define STRIPE_OP_IO 6
+
+/* modifiers to the base operations
+ * STRIPE_OP_MOD_REPAIR_PD - compute the parity block and write it back
+ * STRIPE_OP_MOD_DMA_CHECK - parity is not corrupted by the check
+ */
+#define STRIPE_OP_MOD_REPAIR_PD 7
+#define STRIPE_OP_MOD_DMA_CHECK 8
+
+/*
* Plugging:
*
* To improve write throughput, we need to delay the handling of some