[PATCH 7/7] zram: remove unnecessary lock
From: Minchan Kim
Date: Mon Jan 13 2014 - 06:19:48 EST
read/write lock's performance is really bad compared to
mutex_lock in write most workload.(AFAIR, recenlty there
were some effort to enhance it but not sure it got merged).
Anyway, we don't need such big granuarity read-write lock
any more so this patch replaces read/write lock with mutex.
CPU 12
iozone -t -T -l 12 -u 12 -r 16K -s 60M -I +Z -V 0
==Initial write ==Initial write
records: 10 records: 10
avg: 516189.16 avg: 839907.96
std: 22486.53 std: 47902.17
max: 546970.60 max: 909910.35
min: 481131.54 min: 751148.38
==Rewrite ==Rewrite
records: 10 records: 10
avg: 509527.98 avg: 1050156.37
std: 45799.94 std: 40695.44
max: 611574.27 max: 1111929.26
min: 443679.95 min: 980409.62
==Read ==Read
records: 10 records: 10
avg: 4408624.17 avg: 4472546.76
std: 281152.61 std: 163662.78
max: 4867888.66 max: 4727351.03
min: 4058347.69 min: 4126520.88
==Re-read ==Re-read
records: 10 records: 10
avg: 4462147.53 avg: 4363257.75
std: 283546.11 std: 247292.63
max: 4912894.44 max: 4677241.75
min: 4131386.50 min: 4035235.84
==Reverse Read ==Reverse Read
records: 10 records: 10
avg: 4565865.97 avg: 4485818.08
std: 313395.63 std: 248470.10
max: 5232749.16 max: 4789749.94
min: 4185809.62 min: 3963081.34
==Stride read ==Stride read
records: 10 records: 10
avg: 4515981.80 avg: 4418806.01
std: 211192.32 std: 212837.97
max: 4889287.28 max: 4686967.22
min: 4210362.00 min: 4083041.84
==Random read ==Random read
records: 10 records: 10
avg: 4410525.23 avg: 4387093.18
std: 236693.22 std: 235285.23
max: 4713698.47 max: 4669760.62
min: 4057163.62 min: 3952002.16
==Mixed workload ==Mixed workload
records: 10 records: 10
avg: 243234.25 avg: 2818677.27
std: 28505.07 std: 195569.70
max: 288905.23 max: 3126478.11
min: 212473.16 min: 2484150.69
==Random write ==Random write
records: 10 records: 10
avg: 555887.07 avg: 1053057.79
std: 70841.98 std: 35195.36
max: 683188.28 max: 1096125.73
min: 437299.57 min: 992481.93
==Pwrite ==Pwrite
records: 10 records: 10
avg: 501745.93 avg: 810363.09
std: 16373.54 std: 19245.01
max: 518724.52 max: 833359.70
min: 464208.73 min: 765501.87
==Pread ==Pread
records: 10 records: 10
avg: 4539894.60 avg: 4457680.58
std: 197094.66 std: 188965.60
max: 4877170.38 max: 4689905.53
min: 4226326.03 min: 4095739.72
Read side seem to be a bit slower than old but I believe it's not
bad deal if we consider increased performance of write side and
code readability.
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 17 ++++++++---------
drivers/block/zram/zram_drv.h | 4 +---
2 files changed, 9 insertions(+), 12 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index f1a3c95..011e55d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -230,6 +230,7 @@ static struct zram_meta *zram_meta_alloc(u64 disksize)
}
rwlock_init(&meta->tb_lock);
+ mutex_init(&meta->buffer_lock);
return meta;
free_table:
@@ -412,6 +413,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
struct page *page;
unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
struct zram_meta *meta = zram->meta;
+ bool locked = false;
page = bvec->bv_page;
src = meta->compress_buffer;
@@ -431,6 +433,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
goto out;
}
+ mutex_lock(&meta->buffer_lock);
+ locked = true;
user_mem = kmap_atomic(page);
if (is_partial_io(bvec)) {
@@ -457,7 +461,6 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
meta->compress_workmem);
-
if (!is_partial_io(bvec)) {
kunmap_atomic(user_mem);
user_mem = NULL;
@@ -514,6 +517,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
atomic_inc(&zram->stats.good_compress);
out:
+ if (locked)
+ mutex_unlock(&meta->buffer_lock);
if (is_partial_io(bvec))
kfree(uncmem);
@@ -527,15 +532,10 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
{
int ret;
- if (rw == READ) {
- down_read(&zram->lock);
+ if (rw == READ)
ret = zram_bvec_read(zram, bvec, index, offset, bio);
- up_read(&zram->lock);
- } else {
- down_write(&zram->lock);
+ else
ret = zram_bvec_write(zram, bvec, index, offset);
- up_write(&zram->lock);
- }
return ret;
}
@@ -808,7 +808,6 @@ static int create_device(struct zram *zram, int device_id)
{
int ret = -ENOMEM;
- init_rwsem(&zram->lock);
init_rwsem(&zram->init_lock);
zram->queue = blk_alloc_queue(GFP_KERNEL);
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index d876300..ad8aa35 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -88,13 +88,11 @@ struct zram_meta {
void *compress_buffer;
struct table *table;
struct zs_pool *mem_pool;
+ struct mutex buffer_lock; /* protect compress buffers */
};
struct zram {
struct zram_meta *meta;
- struct rw_semaphore lock; /* protect compression buffers,
- * reads and writes
- */
struct request_queue *queue;
struct gendisk *disk;
int init_done;
--
1.8.4.3
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