dm-kcopyd: Delayed unplug of queues
This patch improves performance aby about 20% when writing to the snapshot
origin. We keep track of two block devices to unplug (one for read and the
other for write) and unplug them when exiting "do_work" thread. If there are
more devices used (in theory it could happen, in practice it is rare), we
unplug immediatelly.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm-kcopyd.c | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)
Index: linux-2.6.34-fast/drivers/md/dm-kcopyd.c
===================================================================
--- linux-2.6.34-fast.orig/drivers/md/dm-kcopyd.c 2010-07-22 16:08:36.000000000 +0200
+++ linux-2.6.34-fast/drivers/md/dm-kcopyd.c 2010-07-22 16:40:19.000000000 +0200
@@ -37,6 +37,8 @@ struct dm_kcopyd_client {
unsigned int nr_pages;
unsigned int nr_free_pages;
+ struct block_device *unplug[2];
+
struct dm_io_client *io_client;
wait_queue_head_t destroyq;
@@ -308,6 +310,23 @@ static int run_complete_job(struct kcopy
return 0;
}
+static void unplug(struct dm_kcopyd_client *kc, int queue)
+{
+ if (kc->unplug[queue] != NULL) {
+ blk_unplug(bdev_get_queue(kc->unplug[queue]));
+ kc->unplug[queue] = NULL;
+ }
+}
+
+static void prepare_unplug(struct dm_kcopyd_client *kc, int queue,
+ struct block_device *bdev)
+{
+ if (likely(kc->unplug[queue] == bdev))
+ return;
+ unplug(kc, queue);
+ kc->unplug[queue] = bdev;
+}
+
static void complete_io(unsigned long error, void *context)
{
struct kcopyd_job *job = (struct kcopyd_job *) context;
@@ -345,7 +364,7 @@ static int run_io_job(struct kcopyd_job
{
int r;
struct dm_io_request io_req = {
- .bi_rw = job->rw | (1 << BIO_RW_UNPLUG),
+ .bi_rw = job->rw,
.mem.type = DM_IO_PAGE_LIST,
.mem.ptr.pl = job->pages,
.mem.offset = job->offset,
@@ -354,10 +373,16 @@ static int run_io_job(struct kcopyd_job
.client = job->kc->io_client,
};
- if (job->rw == READ)
+ if (job->rw == READ) {
r = dm_io(&io_req, 1, &job->source, NULL);
- else
+ prepare_unplug(job->kc, READ, job->source.bdev);
+ } else {
+ if (unlikely(job->num_dests > 1))
+ io_req.bi_rw |= 1 << BIO_RW_UNPLUG;
r = dm_io(&io_req, job->num_dests, job->dests, NULL);
+ if (likely(!(io_req.bi_rw & (1 << BIO_RW_UNPLUG))))
+ prepare_unplug(job->kc, WRITE, job->dests[0].bdev);
+ }
return r;
}
@@ -439,6 +464,8 @@ static void do_work(struct work_struct *
process_jobs(&kc->complete_jobs, kc, run_complete_job);
process_jobs(&kc->pages_jobs, kc, run_pages_job);
process_jobs(&kc->io_jobs, kc, run_io_job);
+ unplug(kc, READ);
+ unplug(kc, WRITE);
}
/*
@@ -619,6 +646,8 @@ int dm_kcopyd_client_create(unsigned int
INIT_LIST_HEAD(&kc->io_jobs);
INIT_LIST_HEAD(&kc->pages_jobs);
+ memset(kc->unplug, 0, sizeof kc->unplug);
+
kc->job_pool = mempool_create_slab_pool(MIN_JOBS, _job_cache);
if (!kc->job_pool)
goto bad_slab;
--
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