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Subject[PATCH] blk: optimize blk_trace macros for cgroup case
Date
Usually blk_trace is not active, but cfq_log_xxx macros unconditionally
prepare cgroup path via blkg_path() which is suboptimal. This provoke
significant performance overhead

## Test
#modprobe null_blk queue_mode=1
#echo cfq > /sys/block/nullb0/queue/scheduler
#fio --ioengine=libaio --direct=1 --group_reporting --filename=/dev/nullb0 \
--rw=write --iodepth=64 --bs=4k --numjobs=8 --size=4G
| | baseline | w/ patch | gain |
| WR iops | 161483 | 189989 | +17% |
| stddev | 14.36 | 13.19 | |

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
block/blk-throttle.c | 17 ++++++++---------
block/cfq-iosched.c | 22 +++++++++++++---------
include/linux/blktrace_api.h | 5 +++++
3 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 5b9c6d5..6ce9750 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -238,21 +238,20 @@ static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
* The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
* throtl_grp; otherwise, just "throtl".
*
- * TODO: this should be made a function and name formatting should happen
- * after testing whether blktrace is enabled.
*/
#define throtl_log(sq, fmt, args...) do { \
struct throtl_grp *__tg = sq_to_tg((sq)); \
struct throtl_data *__td = sq_to_td((sq)); \
\
- (void)__td; \
- if ((__tg)) { \
- char __pbuf[128]; \
+ if (is_blk_trace_active(__td->queue)) { \
+ if ((__tg)) { \
+ char __pbuf[128]; \
\
- blkg_path(tg_to_blkg(__tg), __pbuf, sizeof(__pbuf)); \
- blk_add_trace_msg(__td->queue, "throtl %s " fmt, __pbuf, ##args); \
- } else { \
- blk_add_trace_msg(__td->queue, "throtl " fmt, ##args); \
+ blkg_path(tg_to_blkg(__tg), __pbuf, sizeof(__pbuf)); \
+ blk_add_trace_msg(__td->queue, "throtl %s " fmt, __pbuf, ##args); \
+ } else { \
+ blk_add_trace_msg(__td->queue, "throtl " fmt, ##args); \
+ } \
} \
} while (0)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 5da8e6e..7b90897 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -625,20 +625,24 @@ static inline void cfqg_put(struct cfq_group *cfqg)
}

#define cfq_log_cfqq(cfqd, cfqq, fmt, args...) do { \
- char __pbuf[128]; \
+ if (is_blk_trace_active((cfqd)->queue)) { \
+ char __pbuf[128]; \
\
- blkg_path(cfqg_to_blkg((cfqq)->cfqg), __pbuf, sizeof(__pbuf)); \
- blk_add_trace_msg((cfqd)->queue, "cfq%d%c%c %s " fmt, (cfqq)->pid, \
- cfq_cfqq_sync((cfqq)) ? 'S' : 'A', \
- cfqq_type((cfqq)) == SYNC_NOIDLE_WORKLOAD ? 'N' : ' ',\
- __pbuf, ##args); \
+ blkg_path(cfqg_to_blkg((cfqq)->cfqg), __pbuf, sizeof(__pbuf)); \
+ blk_add_trace_msg((cfqd)->queue, "cfq%d%c%c %s " fmt, (cfqq)->pid, \
+ cfq_cfqq_sync((cfqq)) ? 'S' : 'A', \
+ cfqq_type((cfqq)) == SYNC_NOIDLE_WORKLOAD ? 'N' : ' ', \
+ __pbuf, ##args); \
+ } \
} while (0)

#define cfq_log_cfqg(cfqd, cfqg, fmt, args...) do { \
- char __pbuf[128]; \
+ if (is_blk_trace_active((cfqd)->queue)) { \
+ char __pbuf[128]; \
\
- blkg_path(cfqg_to_blkg(cfqg), __pbuf, sizeof(__pbuf)); \
- blk_add_trace_msg((cfqd)->queue, "%s " fmt, __pbuf, ##args); \
+ blkg_path(cfqg_to_blkg(cfqg), __pbuf, sizeof(__pbuf)); \
+ blk_add_trace_msg((cfqd)->queue, "%s " fmt, __pbuf, ##args); \
+ } \
} while (0)

static inline void cfqg_stats_update_io_add(struct cfq_group *cfqg,
diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h
index afc1343..2981c9e 100644
--- a/include/linux/blktrace_api.h
+++ b/include/linux/blktrace_api.h
@@ -28,6 +28,11 @@ struct blk_trace {
atomic_t dropped;
};

+static inline bool is_blk_trace_active(struct request_queue *q)
+{
+ return q->blk_trace;
+}
+
extern int blk_trace_ioctl(struct block_device *, unsigned, char __user *);
extern void blk_trace_shutdown(struct request_queue *);
extern int do_blk_trace_setup(struct request_queue *q, char *name,
--
1.7.1


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