The commit is pushed to "branch-rh7-3.10.0-1160.36.2.vz7.182.x-ovz" and will
appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.36.2.vz7.182.1
------>
commit 54b4ddbd65f89be6a31c08e2add004d27c79ceed
Author: Kirill Tkhai <[email protected]>
Date: Tue Aug 24 14:39:48 2021 +0300
ploop: Check disable_merge only if there is a delta with such method
There is high spinlock contention on NVME in this place.
But really, we should try this optimization only if it's
there is a delta, which provides such method. Kaio does
not provide it, so here is just spinlock taking wasting.
Signed-off-by: Kirill Tkhai <[email protected]>
---
drivers/block/ploop/dev.c | 31 ++++++++++++++++++++-----------
1 file changed, 20 insertions(+), 11 deletions(-)
diff --git a/drivers/block/ploop/dev.c b/drivers/block/ploop/dev.c
index c4cb944..9abce6a 100644
--- a/drivers/block/ploop/dev.c
+++ b/drivers/block/ploop/dev.c
@@ -1248,18 +1248,27 @@ ploop_merge_bvec(struct request_queue *q, struct
bvec_merge_data *bm_data,
return 0;
}
- /* We can return ret right now, the further action is an optimization
- * to prevent splitting overhead and to enable fast path.
- */
- spin_lock_irqsave(&plo->lock, flags);
- delta = ploop_fast_lookup(plo, sec, 0, &isector);
- if (delta &&
- delta->io.ops->disable_merge &&
- delta->io.ops->disable_merge(&delta->io, isector, len)) {
- plo->st.merge_neg_disable++;
- ret = 0;
+ if (plo->has_disable_merge) {
+ /*
+ * We can return ret right now, the further action
+ * is an optimization to prevent splitting overhead
+ * and to enable fast path.
+ * We do that only in case of there is a delta
+ * with disable_merge method: otherwise this just
+ * brings spinlock taking overhead (seen on NVME).
+ * Since below is only optimization, we check
+ * plo->has_disable_merge without any synchronization.
+ */
+ spin_lock_irqsave(&plo->lock, flags);
+ delta = ploop_fast_lookup(plo, sec, 0, &isector);
+ if (delta &&
+ delta->io.ops->disable_merge &&
+ delta->io.ops->disable_merge(&delta->io, isector, len)) {
+ plo->st.merge_neg_disable++;
+ ret = 0;
+ }
+ spin_unlock_irqrestore(&plo->lock, flags);
}
- spin_unlock_irqrestore(&plo->lock, flags);
/* If no mapping is available, merge up to cluster boundary */
return ret;
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