Re: Mainline kernel OLTP performance update

Jens Axboe
2009-01-22T11:31:30Z

On Wed, Jan 21 2009, Chilukuri, Harita wrote:
> Jen, we work with Matthew on the OLTP workload and have tested the part_stats patch on 2.6.29-rc2. Below are the details:
>
> Disabling the part_stats has positive impact on the OLTP workload.
>
> Linux OLTP Performance summary
> Kernel# Speedup(x) Intr/s CtxSw/s us% sys% idle% iowait%
> 2.6.29-rc2-part_stats 1.000 30329 41716 74 26 0 0
> 2.6.29-rc2-disable-part_stats 1.006 30413 42582 74 25 0 0
>
> Server configurations:
> Intel Xeon Quad-core 2.0GHz 2 cpus/8 cores/8 threads
> 64GB memory, 3 qle2462 FC HBA, 450 spindles (30 logical units)
>
>
> ======oprofile CPU_CLK_UNHALTED for top 30 functions
> Cycles% 2.6.29-rc2-part_stats Cycles% 2.6.29-rc2-disable-part_stats
> 0.9634 qla24xx_intr_handler 1.0372 qla24xx_intr_handler
> 0.9057 copy_user_generic_string 0.7461 qla24xx_wrt_req_reg
> 0.7583 unmap_vmas 0.7130 kmem_cache_alloc
> 0.6280 qla24xx_wrt_req_reg 0.6876 copy_user_generic_string
> 0.6088 kmem_cache_alloc 0.5656 qla24xx_start_scsi
> 0.5468 clear_page_c 0.4881 __blockdev_direct_IO
> 0.5191 qla24xx_start_scsi 0.4728 try_to_wake_up
> 0.4892 try_to_wake_up 0.4588 unmap_vmas
> 0.4870 __blockdev_direct_IO 0.4360 scsi_request_fn
> 0.4187 scsi_request_fn 0.3711 __switch_to
> 0.3717 __switch_to 0.3699 aio_complete
> 0.3567 rb_get_reader_page 0.3648 rb_get_reader_page
> 0.3396 aio_complete 0.3597 ring_buffer_consume
> 0.3012 __end_that_request_first 0.3292 memset_c
> 0.2926 memset_c 0.3076 __list_add
> 0.2926 ring_buffer_consume 0.2771 clear_page_c
> 0.2884 page_remove_rmap 0.2745 task_rq_lock
> 0.2691 disk_map_sector_rcu 0.2733 generic_make_request
> 0.2670 copy_page_c 0.2555 tcp_sendmsg
> 0.2670 lock_timer_base 0.2529 qla2x00_process_completed_re
> 0.2606 qla2x00_process_completed_re0.2440 e1000_xmit_frame
> 0.2521 task_rq_lock 0.2390 lock_timer_base
> 0.2328 __list_add 0.2364 qla24xx_queuecommand
> 0.2286 generic_make_request 0.2301 kmem_cache_free
> 0.2286 pick_next_highest_task_rt 0.2262 blk_queue_end_tag
> 0.2136 push_rt_task 0.2262 kref_get
> 0.2115 blk_queue_end_tag 0.2250 push_rt_task
> 0.2115 kmem_cache_free 0.2135 scsi_dispatch_cmd
> 0.2051 e1000_xmit_frame 0.2084 sd_prep_fn
> 0.2051 scsi_device_unbusy 0.2059 kfree

Alright, so that 0.6%. IIRC, 0.1% (or there abouts) is significant with
this benchmark, correct? To get a feel for the rest of the accounting
overhead, could you try with this patch that just disables the whole
thing?

diff --git a/block/blk-core.c b/block/blk-core.c
index a824e49..eec9126 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -64,6 +64,7 @@ static struct workqueue_struct *kblockd_workqueue;

static void drive_stat_acct(struct request *rq, int new_io)
{
+#if 0
struct hd_struct *part;
int rw = rq_data_dir(rq);
int cpu;
@@ -82,6 +83,7 @@ static void drive_stat_acct(struct request *rq, int new_io)
}

part_stat_unlock();
+#endif
}

void blk_queue_congestion_threshold(struct request_queue *q)
@@ -1014,6 +1017,7 @@ static inline void add_request(struct request_queue *q, struct request *req)
__elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
}

+#if 0
static void part_round_stats_single(int cpu, struct hd_struct *part,
unsigned long now)
{
@@ -1027,6 +1031,7 @@ static void part_round_stats_single(int cpu, struct hd_struct *part,
}
part->stamp = now;
}
+#endif

/**
* part_round_stats() - Round off the performance stats on a struct disk_stats.
@@ -1046,11 +1051,13 @@ static void part_round_stats_single(int cpu, struct hd_struct *part,
*/
void part_round_stats(int cpu, struct hd_struct *part)
{
+#if 0
unsigned long now = jiffies;

if (part->partno)
part_round_stats_single(cpu, &part_to_disk(part)->part0, now);
part_round_stats_single(cpu, part, now);
+#endif
}
EXPORT_SYMBOL_GPL(part_round_stats);

@@ -1690,6 +1697,7 @@ static int __end_that_request_first(struct request *req, int error,
(unsigned long long)req->sector);
}

+#if 0
if (blk_fs_request(req) && req->rq_disk) {
const int rw = rq_data_dir(req);
struct hd_struct *part;
@@ -1700,6 +1708,7 @@ static int __end_that_request_first(struct request *req, int error,
part_stat_add(cpu, part, sectors[rw], nr_bytes >> 9);
part_stat_unlock();
}
+#endif

total_bytes = bio_nbytes = 0;
while ((bio = req->bio) != NULL) {
@@ -1779,7 +1788,9 @@ static int __end_that_request_first(struct request *req, int error,
*/
static void end_that_request_last(struct request *req, int error)
{
+#if 0
struct gendisk *disk = req->rq_disk;
+#endif

if (blk_rq_tagged(req))
blk_queue_end_tag(req->q, req);
@@ -1797,6 +1808,7 @@ static void end_that_request_last(struct request *req, int error)
* IO on queueing nor completion. Accounting the containing
* request is enough.
*/
+#if 0
if (disk && blk_fs_request(req) && req != &req->q->bar_rq) {
unsigned long duration = jiffies - req->start_time;
const int rw = rq_data_dir(req);
@@ -1813,6 +1825,7 @@ static void end_that_request_last(struct request *req, int error)

part_stat_unlock();
}
+#endif

if (req->end_io)
req->end_io(req, error);

--
Jens Axboe