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authorMikulas Patocka <mpatocka@redhat.com>2011-01-13 19:59:50 +0000
committerAlasdair G Kergon <agk@redhat.com>2011-01-13 19:59:50 +0000
commit8d35d3e37eed884ba15229a146df846f399909b4 (patch)
tree795c77c941229f413750e99242f1b2199bebe7a1 /drivers
parent4a038677df4da84e42fd68b5ab2dfa4d82baa444 (diff)
dm kcopyd: delay unplugging
Make kcopyd merge more I/O requests by using device unplugging. Without this patch, each I/O request is dispatched separately to the device. If the device supports tagged queuing, there are many small requests sent to the device. To improve performance, this patch will batch as many requests as possible, allowing the queue to merge consecutive requests, and send them to the device at once. In my tests (15k SCSI disk), this patch improves sequential write throughput: Sequential write throughput (chunksize of 4k, 32k, 512k) unpatched: 15.2, 18.5, 17.5 MB/s patched: 14.4, 22.6, 23.0 MB/s In most common uses (snapshot or two-way mirror), kcopyd is only used for two devices, one for reading and the other for writing, thus this optimization is implemented only for two devices. The optimization may be extended to n-way mirrors with some code complexity increase. 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 immediately. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/md/dm-kcopyd.c54
1 files changed, 51 insertions, 3 deletions
diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c
index 5ad9231c8700..dad32f8bce7d 100644
--- a/drivers/md/dm-kcopyd.c
+++ b/drivers/md/dm-kcopyd.c
@@ -37,6 +37,13 @@ struct dm_kcopyd_client {
unsigned int nr_pages;
unsigned int nr_free_pages;
+ /*
+ * Block devices to unplug.
+ * Non-NULL pointer means that a block device has some pending requests
+ * and needs to be unplugged.
+ */
+ struct block_device *unplug[2];
+
struct dm_io_client *io_client;
wait_queue_head_t destroyq;
@@ -308,6 +315,31 @@ static int run_complete_job(struct kcopyd_job *job)
return 0;
}
+/*
+ * Unplug the block device at the specified index.
+ */
+static void unplug(struct dm_kcopyd_client *kc, int rw)
+{
+ if (kc->unplug[rw] != NULL) {
+ blk_unplug(bdev_get_queue(kc->unplug[rw]));
+ kc->unplug[rw] = NULL;
+ }
+}
+
+/*
+ * Prepare block device unplug. If there's another device
+ * to be unplugged at the same array index, we unplug that
+ * device first.
+ */
+static void prepare_unplug(struct dm_kcopyd_client *kc, int rw,
+ struct block_device *bdev)
+{
+ if (likely(kc->unplug[rw] == bdev))
+ return;
+ unplug(kc, rw);
+ kc->unplug[rw] = bdev;
+}
+
static void complete_io(unsigned long error, void *context)
{
struct kcopyd_job *job = (struct kcopyd_job *) context;
@@ -345,7 +377,7 @@ static int run_io_job(struct kcopyd_job *job)
{
int r;
struct dm_io_request io_req = {
- .bi_rw = job->rw | REQ_UNPLUG,
+ .bi_rw = job->rw,
.mem.type = DM_IO_PAGE_LIST,
.mem.ptr.pl = job->pages,
.mem.offset = job->offset,
@@ -354,10 +386,16 @@ static int run_io_job(struct kcopyd_job *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 (job->num_dests > 1)
+ io_req.bi_rw |= REQ_UNPLUG;
r = dm_io(&io_req, job->num_dests, job->dests, NULL);
+ if (!(io_req.bi_rw & REQ_UNPLUG))
+ prepare_unplug(job->kc, WRITE, job->dests[0].bdev);
+ }
return r;
}
@@ -435,10 +473,18 @@ static void do_work(struct work_struct *work)
* Pages jobs when successful will jump onto the io jobs
* list. io jobs call wake when they complete and it all
* starts again.
+ *
+ * Note that io_jobs add block devices to the unplug array,
+ * this array is cleared with "unplug" calls. It is thus
+ * forbidden to run complete_jobs after io_jobs and before
+ * unplug because the block device could be destroyed in
+ * job completion callback.
*/
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 +665,8 @@ int dm_kcopyd_client_create(unsigned int nr_pages,
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;