Hi Hiro, we have noticed severe performance loss with HT enabled under
FreeBSD but not with MySQL. However, we could be having problems with
MySQL as well without knowing as we haven't done any testing as it is
operating fine. What operating system are you running?
We now disable HT on all servers wherever possible..
Atle
-
Flying Crocodile Inc, Unix Systems Administrator
On Thu, 2 Mar 2006, Hiro Yoshioka wrote:
> Hi,
>
> We found a severe performance degradation when Hyperthreading is on
> and thread_concurrency=20.
>
> We are using OSDL DBT-1 as the benchmark and got about 200 to 250
> BT (bogotransactions per second) HT is OFF normal case but 30 to
> 50 BT on HT is ON.
>
> innodb_thread_concurrency=20
>
> So we did profile (using oprofile tool) and got the following profiling
> data. My impression is that mutex_spin_wait (and ut_delay) is
> something wrong if HT is ON. (Spin-wait loop is too expensive if it is
> hyperthreading.)
>
> I added the following code but it does not help it.
>
> $ diff -pu ut0ut.c.orig ut0ut.c
> --- ut0ut.c.orig 2005-10-17 10:27:43.000000000 +0900
> +++ ut0ut.c 2006-02-28 11:59:16.777840496 +0900
> @@ -290,6 +290,13 @@ ut_delay(
> j = 0;
>
> for (i = 0; i < delay * 50; i++) {
> + /* When executing a spin-wait loop on the Hyper-Threading
> + processor, the processor can suffer a severe performance
> + penalty. The pause instruction provides a hint to the
> + processor. Please refer IA-32 Intel Architecture
> + Software Developers Manual, Vol 3. */
> + __asm__ __volatile__(
> + "pause; \n");
> j += i;
> }
>
> What do you think? Is there any hints?
>
> HT is OFF
> CPU: P4 / Xeon, speed 2793.26 MHz (estimated)
> Counted GLOBAL_POWER_EVENTS events (time during which processor is not
> stopped) with a unit mask of 0x01 (mandatory)
> count 100000
> samples % image name app name symbol
> name
> 13159082 8.8445 libc-2.3.4.so libc-2.3.4.so memcpy
> 12565549 8.4456 libpthread-2.3.4.so libpthread-2.3.4.so
> pthread_mutex_trylock
> 11387363 7.6537 mysqld mysqld
> rec_get_offsets_func
> 9631916 6.4738 libpthread-2.3.4.so libpthread-2.3.4.so
> pthread_mutex_unlock
> 8794484 5.9110 mysqld mysqld
> btr_search_guess_on_hash
> 4949248 3.3265 mysqld mysqld
> row_search_for_mysql
> 4022481 2.7036 mysqld mysqld ut_delay
> 3754265 2.5233 mysqld mysqld
> cmp_dtuple_rec_with_match
> 2535190 1.7040 mysqld mysqld
> row_sel_store_mysql_rec
> 2520957 1.6944 mysqld mysqld
> btr_cur_search_to_nth_level
>
> HT is ON
> CPU: P4 / Xeon with 2 hyper-threads, speed 2793.26 MHz (estimated)
> Counted GLOBAL_POWER_EVENTS events (time during which processor is not
> stopped) with a unit mask of 0x01 (mandatory)
> count 100000
> samples % image name app name symbol
> name
> 53221317 21.4225 libpthread-2.3.4.so libpthread-2.3.4.so
> pthread_mutex_lock
> 25743323 10.3621 mysqld mysqld ut_delay
> 12345146 4.9691 vmlinux vmlinux do_futex
> 12066038 4.8568 mysqld mysqld
> mutex_spin_wait
> 10395391 4.1843 vmlinux vmlinux
> LKST_ETYPE_PROCESS_SCHED_ENTER_HEADER_hook
> 9247281 3.7222 libpthread-2.3.4.so libpthread-2.3.4.so
> pthread_mutex_unlock
> 7407229 2.9815 vmlinux vmlinux
> futex_requeue
> 5921454 2.3835 libpthread-2.3.4.so libpthread-2.3.4.so
> pthread_mutex_trylock
> 5484279 2.2075 vmlinux vmlinux
> LKST_ETYPE_PROCESS_WAKEUP_HEADER_hook
> 4846067 1.9506 vmlinux vmlinux
> __switch_to
>
> Regards,
> Hiro
>
>
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