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Yasufumi,

This is SSD card, 800 can not be too large.

-- 
performance regression in tpc-c  1 thread
https://bugs.launchpad.net/bugs/326464
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Status in Patches for MySQL by Percona: Confirmed
Status in Percona XtraDB Storage Engine for MySQL: In Progress

Bug description:
I observe performance regression if run XtraDB (the same for percona patches in 5.0.75) with IO tuned parameters in 1 thread tpc-c benchmarks. With 4 threads = results are OK.

tuned parameters:

innodb_write_io_threads=4
innodb_read_io_threads=4
innodb_io_capacity=800
innodb_adaptive_checkpoint=1


full my.cnf:

====
[mysqld]
#mysqld options in alphabetical order
user=root

default_table_type=MYISAM

innodb_buffer_pool_size=3G
innodb_data_file_path=ibdata1:10M:autoextend
innodb_file_per_table=1
innodb_flush_log_at_trx_commit=1
innodb_log_buffer_size=8M
innodb_log_files_in_group=2
innodb_log_file_size=128M
innodb_thread_concurrency=0
innodb_flush_method = O_DIRECT

innodb_write_io_threads=4
innodb_read_io_threads=4
innodb_io_capacity=800
innodb_adaptive_checkpoint=1

#innodb_extra_rsegments=16
#innodb_thread_concurrency=16

max_connections=3000
query_cache_size=0
skip-name-resolve

table_cache=2048

===

I use tpc-c 100W.

for 1 thread not tuned I have 3483.8 TpmC 
tuned - 3156.6

for 10 threads:
not tuned: 8039.1
tuned: 9111.9

So we have something wrong in 1-thread case.