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dm thin: direct dispatch when breaking sharing 

This use of direct submission in process_shared_bio() reduces latency
for submitting bios in the shared cell by avoiding adding those bios to
the deferred list and waiting for the next iteration of the worker.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Joe Thornber 2014-10-15 14:46:58 +01:00 committed by Mike Snitzer
parent 2d759a46b4
commit 23ca2bb6c6
1 changed files with 57 additions and 13 deletions
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70
drivers/md/dm-thin.c
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@ -1390,11 +1390,53 @@ static void break_sharing(struct thin_c *tc, struct bio *bio, dm_block_t block,
}
}
static void __remap_and_issue_shared_cell(void *context,
struct dm_bio_prison_cell *cell)
{
struct remap_info *info = context;
struct bio *bio;
while ((bio = bio_list_pop(&cell->bios))) {
if ((bio_data_dir(bio) == WRITE) ||
(bio->bi_rw & (REQ_DISCARD | REQ_FLUSH | REQ_FUA)))
bio_list_add(&info->defer_bios, bio);
else {
struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));;
h->shared_read_entry = dm_deferred_entry_inc(info->tc->pool->shared_read_ds);
inc_all_io_entry(info->tc->pool, bio);
bio_list_add(&info->issue_bios, bio);
}
}
}
static void remap_and_issue_shared_cell(struct thin_c *tc,
struct dm_bio_prison_cell *cell,
dm_block_t block)
{
struct bio *bio;
struct remap_info info;
info.tc = tc;
bio_list_init(&info.defer_bios);
bio_list_init(&info.issue_bios);
cell_visit_release(tc->pool, __remap_and_issue_shared_cell,
&info, cell);
while ((bio = bio_list_pop(&info.defer_bios)))
thin_defer_bio(tc, bio);
while ((bio = bio_list_pop(&info.issue_bios)))
remap_and_issue(tc, bio, block);
}
static void process_shared_bio(struct thin_c *tc, struct bio *bio,
dm_block_t block,
struct dm_thin_lookup_result *lookup_result)
struct dm_thin_lookup_result *lookup_result,
struct dm_bio_prison_cell *virt_cell)
{
struct dm_bio_prison_cell *cell;
struct dm_bio_prison_cell *data_cell;
struct pool *pool = tc->pool;
struct dm_cell_key key;
@ -1403,19 +1445,23 @@ static void process_shared_bio(struct thin_c *tc, struct bio *bio,
* of being broken so we have nothing further to do here.
*/
build_data_key(tc->td, lookup_result->block, &key);
if (bio_detain(pool, &key, bio, &cell))
if (bio_detain(pool, &key, bio, &data_cell)) {
cell_defer_no_holder(tc, virt_cell);
return;
}
if (bio_data_dir(bio) == WRITE && bio->bi_iter.bi_size)
break_sharing(tc, bio, block, &key, lookup_result, cell);
else {
if (bio_data_dir(bio) == WRITE && bio->bi_iter.bi_size) {
break_sharing(tc, bio, block, &key, lookup_result, data_cell);
cell_defer_no_holder(tc, virt_cell);
} else {
struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
h->shared_read_entry = dm_deferred_entry_inc(pool->shared_read_ds);
inc_all_io_entry(pool, bio);
cell_defer_no_holder(tc, cell);
remap_and_issue(tc, bio, lookup_result->block);
remap_and_issue_shared_cell(tc, data_cell, lookup_result->block);
remap_and_issue_shared_cell(tc, virt_cell, lookup_result->block);
}
}
@ -1484,11 +1530,9 @@ static void process_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
switch (r) {
case 0:
if (lookup_result.shared) {
process_shared_bio(tc, bio, block, &lookup_result);
// FIXME: we can't remap because we're waiting on a commit
cell_defer_no_holder(tc, cell); /* FIXME: pass this cell into process_shared? */
} else {
if (lookup_result.shared)
process_shared_bio(tc, bio, block, &lookup_result, cell);
else {
inc_all_io_entry(pool, bio);
remap_and_issue(tc, bio, lookup_result.block);
inc_remap_and_issue_cell(tc, cell, lookup_result.block);