From: Keun-young Park <keunyoung@google.com>
Date: Tue, 15 Nov 2016 02:25:15 +0000 (-0800)
Subject: ANDROID: dm verity: add minimum prefetch size
X-Git-Tag: firefly_0821_release~176^2~52
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=26a380b3ce97e6c3919f7ea576b91b23f7e9728c;p=firefly-linux-kernel-4.4.55.git

ANDROID: dm verity: add minimum prefetch size

- For device like eMMC, it gives better performance to read more hash
  blocks at a time.
- For android, set it to default 128.
  For other devices, set it to 1 which is the same as now.
- saved boot-up time by 300ms in tested device

bug: 32246564

Cc: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Keun-young Park <keunyoung@google.com>
---

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 6035794bc1f2..3d237a03dab3 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -458,6 +458,21 @@ config DM_VERITY
 
 	  If unsure, say N.
 
+config DM_VERITY_HASH_PREFETCH_MIN_SIZE_128
+	bool "Prefetch size 128"
+
+config DM_VERITY_HASH_PREFETCH_MIN_SIZE
+	int "Verity hash prefetch minimum size"
+	depends on DM_VERITY
+	range 1 4096
+	default 128 if DM_VERITY_HASH_PREFETCH_MIN_SIZE_128
+	default 1
+	---help---
+	  This sets minimum number of hash blocks to prefetch for dm-verity.
+	  For devices like eMMC, having larger prefetch size like 128 can improve
+	  performance with increased memory consumption for keeping more hashes
+	  in RAM.
+
 config DM_VERITY_FEC
 	bool "Verity forward error correction support"
 	depends on DM_VERITY
@@ -510,6 +525,7 @@ config DM_ANDROID_VERITY
 	depends on ASYMMETRIC_KEY_TYPE
 	depends on ASYMMETRIC_PUBLIC_KEY_SUBTYPE
 	depends on MD_LINEAR
+	select DM_VERITY_HASH_PREFETCH_MIN_SIZE_128
 	---help---
 	  This device-mapper target is virtually a VERITY target. This
 	  target is setup by reading the metadata contents piggybacked
diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 9d3d4b297201..c7e97cf6e7fb 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -501,6 +501,7 @@ static void verity_prefetch_io(struct work_struct *work)
 		container_of(work, struct dm_verity_prefetch_work, work);
 	struct dm_verity *v = pw->v;
 	int i;
+	sector_t prefetch_size;
 
 	for (i = v->levels - 2; i >= 0; i--) {
 		sector_t hash_block_start;
@@ -523,8 +524,14 @@ static void verity_prefetch_io(struct work_struct *work)
 				hash_block_end = v->hash_blocks - 1;
 		}
 no_prefetch_cluster:
+		// for emmc, it is more efficient to send bigger read
+		prefetch_size = max((sector_t)CONFIG_DM_VERITY_HASH_PREFETCH_MIN_SIZE,
+			hash_block_end - hash_block_start + 1);
+		if ((hash_block_start + prefetch_size) >= (v->hash_start + v->hash_blocks)) {
+			prefetch_size = hash_block_end - hash_block_start + 1;
+		}
 		dm_bufio_prefetch(v->bufio, hash_block_start,
-				  hash_block_end - hash_block_start + 1);
+				  prefetch_size);
 	}
 
 	kfree(pw);