[PATCH 001 of 006] raid5: Move write operations to a work queue

From: Dan Williams
Date: Wed Jun 28 2006 - 14:28:37 EST

Next message: Dan Williams: "[PATCH 004 of 006] raid5: Move read completion copies to a workqueue"
Previous message: Andrew Morton: "Re: 2.6.17-mm3: segvs in modpost with out-of-tree modules"
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This patch moves write (reconstruct and read-modify) operations to a
work queue. Note the next patch in this series fixes some incorrect
assumptions around having multiple operations in flight (i.e. ignore
this version of 'queue_raid_work').

Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

drivers/md/raid5.c | 314 +++++++++++++++++++++++++++++++++++++++++----
include/linux/raid/raid5.h | 67 +++++++++
2 files changed, 357 insertions(+), 24 deletions(-)

===================================================================
Index: linux-2.6-raid/drivers/md/raid5.c
===================================================================
--- linux-2.6-raid.orig/drivers/md/raid5.c 2006-06-28 08:44:11.000000000 -0700
+++ linux-2.6-raid/drivers/md/raid5.c 2006-06-28 09:52:07.000000000 -0700
@@ -305,6 +305,7 @@
memset(sh, 0, sizeof(*sh) + (conf->raid_disks-1)*sizeof(struct r5dev));
sh->raid_conf = conf;
spin_lock_init(&sh->lock);
+ INIT_WORK(&sh->ops.work, conf->do_block_ops, sh);

if (grow_buffers(sh, conf->raid_disks)) {
shrink_buffers(sh, conf->raid_disks);
@@ -1224,6 +1225,80 @@
}
}

+static int handle_write_operations5(struct stripe_head *sh, int rcw, int locked)
+{
+ int i, pd_idx = sh->pd_idx, disks = sh->disks;
+ int complete=0;
+
+ if (test_bit(STRIPE_OP_RCW, &sh->state) &&
+ test_bit(STRIPE_OP_RCW_Done, &sh->ops.state)) {
+ clear_bit(STRIPE_OP_RCW, &sh->state);
+ clear_bit(STRIPE_OP_RCW_Done, &sh->ops.state);
+ complete++;
+ }
+
+ if (test_bit(STRIPE_OP_RMW, &sh->state) &&
+ test_bit(STRIPE_OP_RMW_Done, &sh->ops.state)) {
+ clear_bit(STRIPE_OP_RMW, &sh->state);
+ clear_bit(STRIPE_OP_RMW_Done, &sh->ops.state);
+ BUG_ON(++complete == 2);
+ }
+
+
+ /* If no operation is currently in process then use the rcw flag to
+ * select an operation
+ */
+ if (locked == 0) {
+ if (rcw == 0) {
+ /* enter stage 1 of reconstruct write operation */
+ set_bit(STRIPE_OP_RCW, &sh->state);
+ set_bit(STRIPE_OP_RCW_Drain, &sh->ops.state);
+ for (i=disks ; i-- ;) {
+ struct r5dev *dev = &sh->dev[i];
+
+ if (i!=pd_idx && dev->towrite) {
+ set_bit(R5_LOCKED, &dev->flags);
+ locked++;
+ }
+ }
+ } else {
+ /* enter stage 1 of read modify write operation */
+ BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags));
+ set_bit(STRIPE_OP_RMW, &sh->state);
+ set_bit(STRIPE_OP_RMW_ParityPre, &sh->ops.state);
+ for (i=disks ; i-- ;) {
+ struct r5dev *dev = &sh->dev[i];
+ if (i==pd_idx)
+ continue;
+
+ if (dev->towrite &&
+ test_bit(R5_UPTODATE, &dev->flags)) {
+ set_bit(R5_LOCKED, &dev->flags);
+ locked++;
+ }
+ }
+ }
+ } else if (locked && complete == 0) /* the queue has an operation in flight */
+ locked = -EBUSY;
+ else if (complete)
+ locked = 0;
+
+ /* keep the parity disk locked while asynchronous operations
+ * are in flight
+ */
+ if (locked > 0) {
+ set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);
+ clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+ sh->ops.queue_count++;
+ } else if (locked == 0)
+ set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+
+ PRINTK("%s: stripe %llu locked: %d complete: %d op_state: %lx\n",
+ __FUNCTION__, (unsigned long long)sh->sector,
+ locked, complete, sh->ops.state);
+
+ return locked;
+}

/*
@@ -1320,6 +1395,174 @@
return pd_idx;
}

+static inline void drain_bio(struct bio *wbi, sector_t sector, struct page *page)
+{
+ while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
+ copy_data(1, wbi, page, sector);
+ wbi = r5_next_bio(wbi, sector);
+ }
+}
+
+/* must be called under the stripe lock */
+static void queue_raid_work(struct stripe_head *sh)
+{
+ if (--sh->ops.queue_count == 0) {
+ atomic_inc(&sh->count);
+ queue_work(sh->raid_conf->block_ops_queue, &sh->ops.work);
+ } else if (sh->ops.queue_count < 0)
+ sh->ops.queue_count = 0;
+}
+
+/*
+ * raid5_do_soft_block_ops - perform block memory operations on stripe data
+ * outside the spin lock.
+ */
+static void raid5_do_soft_block_ops(void *stripe_head_ref)
+{
+ struct stripe_head *sh = stripe_head_ref;
+ int i, pd_idx = sh->pd_idx, disks = sh->disks, count = 1;
+ void *ptr[MAX_XOR_BLOCKS];
+ struct bio *chosen;
+ int overlap=0, new_work=0, written=0;
+ unsigned long state, ops_state;
+
+ /* take a snapshot of what needs to be done at this point in time */
+ spin_lock(&sh->lock);
+ state = sh->state;
+ ops_state = sh->ops.state;
+ spin_unlock(&sh->lock);
+
+ if (test_bit(STRIPE_OP_RMW, &state)) {
+ PRINTK("%s: stripe %llu STRIPE_OP_RMW op_state: %lx\n",
+ __FUNCTION__, (unsigned long long)sh->sector,
+ ops_state);
+
+ ptr[0] = page_address(sh->dev[pd_idx].page);
+
+ if (test_and_clear_bit(STRIPE_OP_RMW_ParityPre, &ops_state)) {
+ for (i=disks ; i-- ;) {
+ struct r5dev *dev = &sh->dev[i];
+ /* if it is locked then servicing
+ * has been requested
+ */
+ if (dev->towrite && test_bit(R5_LOCKED, &dev->flags)) {
+ ptr[count++] = page_address(dev->page);
+ /* ? is the device_lock necessary here, compute_parity
+ * does not lock for this operation ?
+ */
+ chosen = dev->towrite;
+ dev->towrite = NULL;
+
+ overlap++;
+
+ BUG_ON(dev->written);
+ dev->written = chosen;
+ check_xor();
+ }
+ }
+ if (count != 1)
+ xor_block(count, STRIPE_SIZE, ptr);
+ set_bit(STRIPE_OP_RMW_Drain, &ops_state);
+ }
+ if (test_and_clear_bit(STRIPE_OP_RMW_Drain, &ops_state)) {
+ for (i=disks ; i-- ;) {
+ struct r5dev *dev = &sh->dev[i];
+ written++;
+ drain_bio(dev->written, dev->sector, dev->page);
+ }
+ set_bit(STRIPE_OP_RMW_ParityPost, &ops_state);
+ }
+ if (test_and_clear_bit(STRIPE_OP_RMW_ParityPost, &ops_state)) {
+ for (i=disks ; i-- ;) {
+ struct r5dev *dev = &sh->dev[i];
+ if (dev->written) {
+ ptr[count++] = page_address(dev->page);
+ check_xor();
+ }
+ }
+ if (count != 1)
+ xor_block(count, STRIPE_SIZE, ptr);
+
+ /* signal completion and acknowledge the last state seen
+ * by sh->ops.state
+ */
+ set_bit(STRIPE_OP_RMW_Done, &ops_state);
+ set_bit(STRIPE_OP_RMW_ParityPre, &ops_state);
+ }
+
+ } else if (test_bit(STRIPE_OP_RCW, &state)) {
+ PRINTK("%s: stripe %llu STRIPE_OP_RCW op_state: %lx\n",
+ __FUNCTION__, (unsigned long long)sh->sector,
+ ops_state);
+
+ ptr[0] = page_address(sh->dev[pd_idx].page);
+
+ if (test_and_clear_bit(STRIPE_OP_RCW_Drain, &ops_state)) {
+ for (i=disks ; i-- ;) {
+ struct r5dev *dev = &sh->dev[i];
+ if (i!=pd_idx && dev->towrite &&
+ test_bit(R5_LOCKED, &dev->flags)) {
+ chosen = dev->towrite;
+ dev->towrite = NULL;
+
+ BUG_ON(dev->written);
+ dev->written = chosen;
+
+ overlap++;
+ written++;
+
+ drain_bio(dev->written, dev->sector,
+ dev->page);
+ } else if (i==pd_idx)
+ memset(ptr[0], 0, STRIPE_SIZE);
+ }
+ set_bit(STRIPE_OP_RCW_Parity, &ops_state);
+ }
+ if (test_and_clear_bit(STRIPE_OP_RCW_Parity, &ops_state)) {
+ for (i=disks; i--;)
+ if (i != pd_idx) {
+ ptr[count++] = page_address(sh->dev[i].page);
+ check_xor();
+ }
+ if (count != 1)
+ xor_block(count, STRIPE_SIZE, ptr);
+
+ /* signal completion and acknowledge the last state seen
+ * by sh->ops.state
+ */
+ set_bit(STRIPE_OP_RCW_Done, &ops_state);
+ set_bit(STRIPE_OP_RCW_Drain, &ops_state);
+
+ }
+ }
+
+ spin_lock(&sh->lock);
+ /* Update the state of operations, by XORing we clear the stage 1 requests
+ * while preserving new requests.
+ */
+ sh->ops.state ^= ops_state;
+
+ if (written)
+ for (i=disks ; i-- ;) {
+ struct r5dev *dev = &sh->dev[i];
+ if (dev->written)
+ set_bit(R5_UPTODATE, &dev->flags);
+ }
+
+ if (overlap)
+ 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);
+ }
+
+ sh->ops.queue_count += new_work;
+ set_bit(STRIPE_HANDLE, &sh->state);
+ queue_raid_work(sh);
+ spin_unlock(&sh->lock);
+
+ release_stripe(sh);
+}

/*
* handle_stripe - do things to a stripe.
@@ -1333,7 +1576,6 @@
* schedule a write of some buffers
* return confirmation of parity correctness
*
- * Parity calculations are done inside the stripe lock
* buffers are taken off read_list or write_list, and bh_cache buffers
* get BH_Lock set before the stripe lock is released.
*
@@ -1352,9 +1594,9 @@
int failed_num=0;
struct r5dev *dev;

- PRINTK("handling stripe %llu, cnt=%d, pd_idx=%d\n",
- (unsigned long long)sh->sector, atomic_read(&sh->count),
- sh->pd_idx);
+ PRINTK("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d\n",
+ (unsigned long long)sh->sector, sh->state, atomic_read(&sh->count),
+ sh->pd_idx);

spin_lock(&sh->lock);
clear_bit(STRIPE_HANDLE, &sh->state);
@@ -1596,7 +1838,8 @@
}

/* now to consider writing and what else, if anything should be read */
- if (to_write) {
+ if (to_write || test_bit(STRIPE_OP_RCW, &sh->state) ||
+ test_bit(STRIPE_OP_RMW, &sh->state)) {
int rmw=0, rcw=0;
for (i=disks ; i--;) {
/* would I have to read this buffer for read_modify_write */
@@ -1668,25 +1911,29 @@
}
}
/* now if nothing is locked, and if we have enough data, we can start a write request */
- if (locked == 0 && (rcw == 0 ||rmw == 0) &&
- !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
- PRINTK("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)) {
- PRINTK("Writing block %d\n", i);
- locked++;
- set_bit(R5_Wantwrite, &sh->dev[i].flags);
- if (!test_bit(R5_Insync, &sh->dev[i].flags)
- || (i==sh->pd_idx && failed == 0))
- set_bit(STRIPE_INSYNC, &sh->state);
+ /* ...or, if we have previously started write operations we can now advance the state */
+ if ((locked == 0 && (rcw == 0 ||rmw == 0) &&
+ !test_bit(STRIPE_BIT_DELAY, &sh->state)) ||
+ test_bit(STRIPE_OP_RCW, &sh->state) || test_bit(STRIPE_OP_RMW, &sh->state)) {
+ int work_queued = handle_write_operations5(sh, rcw, locked);
+ if (work_queued == 0) {
+ /* now every locked buffer is ready to be written */
+ for (i=disks; i--;)
+ if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
+ PRINTK("Writing block %d\n", i);
+ locked++;
+ set_bit(R5_Wantwrite, &sh->dev[i].flags);
+ if (!test_bit(R5_Insync, &sh->dev[i].flags)
+ || (i==sh->pd_idx && 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);
}
- 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);
- }
+ } else if (work_queued > 0)
+ locked += work_queued;
}
}

@@ -1819,6 +2066,8 @@
}
}

+ queue_raid_work(sh);
+
spin_unlock(&sh->lock);

while ((bi=return_bi)) {
@@ -1829,6 +2078,7 @@
bi->bi_size = 0;
bi->bi_end_io(bi, bytes, 0);
}
+
for (i=disks; i-- ;) {
int rw;
struct bio *bi;
@@ -3117,6 +3367,21 @@
if (!conf->spare_page)
goto abort;
}
+
+ sprintf(conf->workqueue_name, "%s_raid5_ops",
+ mddev->gendisk->disk_name);
+
+ if ((conf->block_ops_queue = create_workqueue(conf->workqueue_name))
+ == NULL)
+ goto abort;
+
+ /* To Do:
+ * 1/ Offload to asynchronous copy / xor engines
+ * 2/ Automated selection of optimal do_block_ops
+ * routine similar to the xor template selection
+ */
+ conf->do_block_ops = raid5_do_soft_block_ops;
+
spin_lock_init(&conf->device_lock);
init_waitqueue_head(&conf->wait_for_stripe);
init_waitqueue_head(&conf->wait_for_overlap);
@@ -3279,6 +3544,8 @@
safe_put_page(conf->spare_page);
kfree(conf->disks);
kfree(conf->stripe_hashtbl);
+ if (conf->do_block_ops)
+ destroy_workqueue(conf->block_ops_queue);
kfree(conf);
}
mddev->private = NULL;
@@ -3299,6 +3566,7 @@
blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
sysfs_remove_group(&mddev->kobj, &raid5_attrs_group);
kfree(conf->disks);
+ destroy_workqueue(conf->block_ops_queue);
kfree(conf);
mddev->private = NULL;
return 0;
Index: linux-2.6-raid/include/linux/raid/raid5.h
===================================================================
--- linux-2.6-raid.orig/include/linux/raid/raid5.h 2006-06-28 08:44:11.000000000 -0700
+++ linux-2.6-raid/include/linux/raid/raid5.h 2006-06-28 10:34:54.000000000 -0700
@@ -3,6 +3,8 @@

#include <linux/raid/md.h>
#include <linux/raid/xor.h>
+#include <linux/workqueue.h>
+#include <linux/dmaengine.h>

/*
*
@@ -123,6 +125,14 @@
* 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.
+ *
+ * Block operations (copy, xor, block fill, and block compare) are executed
+ * outside the spin lock. A stripe can have multiple operations in flight provided
+ * that the operations do not have data dependencies. For most cases data
+ * dependencies will be avoided by the 'overlap' protection logic in add_stripe_bio.
+ * A case that violates this rule is compute block operations where the work queue must
+ * guarantee that blocks are up to date before proceeding with a write or check
+ * parity operation.
*/

struct stripe_head {
@@ -136,6 +146,16 @@
spinlock_t lock;
int bm_seq; /* sequence number for bitmap flushes */
int disks; /* disks in stripe */
+ struct stripe_operations {
+ int queue_count; /* if == 0 places stripe in the workqueue */
+ unsigned long state; /* state of block operations */
+ struct work_struct work; /* work queue descriptor */
+ #ifdef CONFIG_DMA_ENGINE
+ u32 dma_result; /* storage for dma engine results */
+ dma_cookie_t dma_cookie; /* last issued dma operation */
+ struct dma_chan *dma_chan; /* dma channel for ops offload */
+ #endif
+ } ops;
struct r5dev {
struct bio req;
struct bio_vec vec;
@@ -145,6 +165,7 @@
unsigned long flags;
} dev[1]; /* allocated with extra space depending of RAID geometry */
};
+
/* Flags */
#define R5_UPTODATE 0 /* page contains current data */
#define R5_LOCKED 1 /* IO has been submitted on "req" */
@@ -156,8 +177,9 @@
#define R5_Overlap 7 /* There is a pending overlapping request on this block */
#define R5_ReadError 8 /* seen a read error here recently */
#define R5_ReWrite 9 /* have tried to over-write the readerror */
-
#define R5_Expanded 10 /* This block now has post-expand data */
+#define R5_Consistent 11 /* Block is HW DMA-able without a cache flush */
+
/*
* Write method
*/
@@ -179,6 +201,41 @@
#define STRIPE_EXPANDING 9
#define STRIPE_EXPAND_SOURCE 10
#define STRIPE_EXPAND_READY 11
+#define STRIPE_OP_RCW 12
+#define STRIPE_OP_RMW 13 /* RAID-5 only */
+#define STRIPE_OP_UPDATE 14 /* RAID-6 only */
+#define STRIPE_OP_CHECK 15
+#define STRIPE_OP_COMPUTE 16
+#define STRIPE_OP_COMPUTE2 17 /* RAID-6 only */
+#define STRIPE_OP_BIOFILL 18
+
+/*
+ * These flags are communication markers between the handle_stripe[5|6]
+ * routine and the block operations work queue
+ * - The _End definitions are a signal from handle_stripe to the work queue to
+ * to ensure the completion of the operation so the results can be committed
+ * to disk
+ * - The _Done definitions signal completion from work queue to handle_stripe
+ * - All other definitions are service requests for the work queue
+ */
+#define STRIPE_OP_RCW_Drain 0
+#define STRIPE_OP_RCW_Parity 1
+#define STRIPE_OP_RCW_End 2
+#define STRIPE_OP_RCW_Done 3
+#define STRIPE_OP_RMW_ParityPre 4
+#define STRIPE_OP_RMW_Drain 5
+#define STRIPE_OP_RMW_ParityPost 6
+#define STRIPE_OP_RMW_End 7
+#define STRIPE_OP_RMW_Done 8
+#define STRIPE_OP_CHECK_Gen 9
+#define STRIPE_OP_CHECK_Verify 10
+#define STRIPE_OP_CHECK_End 11
+#define STRIPE_OP_CHECK_Done 12
+#define STRIPE_OP_COMPUTE_Prep 13
+#define STRIPE_OP_COMPUTE_Parity 14
+#define STRIPE_OP_COMPUTE_End 15
+#define STRIPE_OP_COMPUTE_Done 16
+
/*
* Plugging:
*
@@ -229,11 +286,16 @@
atomic_t preread_active_stripes; /* stripes with scheduled io */

atomic_t reshape_stripes; /* stripes with pending writes for reshape */
+
+ struct workqueue_struct *block_ops_queue;
+ void (*do_block_ops)(void *);
+
/* unfortunately we need two cache names as we temporarily have
* two caches.
*/
int active_name;
char cache_name[2][20];
+ char workqueue_name[20];
kmem_cache_t *slab_cache; /* for allocating stripes */

int seq_flush, seq_write;
-
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Next message: Dan Williams: "[PATCH 004 of 006] raid5: Move read completion copies to a workqueue"
Previous message: Andrew Morton: "Re: 2.6.17-mm3: segvs in modpost with out-of-tree modules"
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