Hi
I've made this patch that improves kcopyd latency. When we set the bit
DM_KCOPYD_EARLY_CALLBACK, the completion is called from the interrupt
context instead of process context.
I'd like to ask if you can benchmark it and test if it improves
performance of dm-thin and dm-cache.
Mikulas
Index: linux-2.6/drivers/md/dm-cache-target.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-cache-target.c
+++ linux-2.6/drivers/md/dm-cache-target.c
@@ -1171,9 +1171,9 @@ static void copy(struct dm_cache_migrati
c_region.count = cache->sectors_per_block;
if (promote)
- dm_kcopyd_copy(cache->copier, &o_region, 1, &c_region, 0,
copy_complete, &mg->k);
+ dm_kcopyd_copy(cache->copier, &o_region, 1, &c_region, 1UL <<
DM_KCOPYD_EARLY_CALLBACK, copy_complete, &mg->k);
else
- dm_kcopyd_copy(cache->copier, &c_region, 1, &o_region, 0,
copy_complete, &mg->k);
+ dm_kcopyd_copy(cache->copier, &c_region, 1, &o_region, 1UL <<
DM_KCOPYD_EARLY_CALLBACK, copy_complete, &mg->k);
}
static void bio_drop_shared_lock(struct cache *cache, struct bio *bio)
Index: linux-2.6/drivers/md/dm-kcopyd.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-kcopyd.c
+++ linux-2.6/drivers/md/dm-kcopyd.c
@@ -512,6 +512,10 @@ static int run_complete_job(struct kcopy
return 0;
}
+static void null_completion(int read_err, unsigned long write_err, void
*context)
+{
+}
+
static void complete_io(unsigned long error, void *context)
{
struct kcopyd_job *job = (struct kcopyd_job *) context;
@@ -532,10 +536,13 @@ static void complete_io(unsigned long er
}
}
- if (op_is_write(job->rw))
+ if (op_is_write(job->rw)) {
+ if (test_bit(DM_KCOPYD_EARLY_CALLBACK, &job->flags)) {
+ job->fn(job->read_err, job->write_err, job->context);
+ job->fn = null_completion;
+ }
push(&kc->complete_jobs, job);
-
- else {
+ } else {
job->rw = WRITE;
push(&kc->io_jobs, job);
}
@@ -735,6 +742,7 @@ static void segment_complete(int read_er
sub_job->dests[i].count = count;
}
+ sub_job->flags &= ~(1UL << DM_KCOPYD_EARLY_CALLBACK);
sub_job->fn = segment_complete;
sub_job->context = sub_job;
dispatch_job(sub_job);
Index: linux-2.6/drivers/md/dm-thin.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-thin.c
+++ linux-2.6/drivers/md/dm-thin.c
@@ -1359,7 +1359,7 @@ static void schedule_copy(struct thin_c
to.count = len;
dm_kcopyd_copy(pool->copier, &from, 1, &to,
- 0, copy_complete, m);
+ 1UL << DM_KCOPYD_EARLY_CALLBACK, copy_complete,
m);
/*
* Do we need to zero a tail region?
Index: linux-2.6/include/linux/dm-kcopyd.h
===================================================================
--- linux-2.6.orig/include/linux/dm-kcopyd.h
+++ linux-2.6/include/linux/dm-kcopyd.h
@@ -19,8 +19,9 @@
/* FIXME: make this configurable */
#define DM_KCOPYD_MAX_REGIONS 8
-#define DM_KCOPYD_IGNORE_ERROR 1
-#define DM_KCOPYD_WRITE_SEQ 2
+#define DM_KCOPYD_IGNORE_ERROR 1
+#define DM_KCOPYD_WRITE_SEQ 2
+#define DM_KCOPYD_EARLY_CALLBACK 3
struct dm_kcopyd_throttle {
unsigned throttle;
--
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