Re: hyperthreading performance with dbt-2 on 2.6.0-test11

[Nick Piggin <piggin@cyberone.com.au>]

Mark Wong wrote:

>On Tue, Dec 09, 2003 at 11:17:26AM +1100, Nick Piggin wrote:
>
>>
>>markw@osdl.org wrote:
>>
>>
>>>Hello, I have some data with hyperthreading I wanted to share.
>>>
>>>I've seen about a 15% performance decrease in performance on a 4-way
>>>Xeon system when I enable hyperthreading for my DBT-2 workload.  I also
>>>gave Ingo's test11-C1 patch that someone pointed me to a try and only
>>>saw a 12% decrease. Has anyone found this to be common with any specific
>>>workloads?
>>>
>>>I'm not really sure what to look for, but I do see some changes in the
>>>readprofile data, which I've copied in part below.  It appears that the
>>>count of schedule, __make_request, and try_to_wake_up are the only
>>>functions at the top of the profile that are significantly different.
>>>The links I have posted also have pointers to oprofile data as well as
>>>annotated assembly source output, if that interests anyone.  If I can
>>>provide any other details, let me know.
>>>
>>>
>>Hi Mark,
>>It could be cache contention which I think is typically the reason
>>hyperthreading can hurt performance. Its basically impossible for
>>the scheduler to correct this automatically (access to performance
>>counters might make it slightly less impossible).
>>
>>Probably the CPU hotplug interface would enable a tool to effectively
>>turn HT on or off and it would be up to an administrator to tune
>>performance.
>>
>>You could try my scheduler patchset if you like. I have recently got
>>HT support working (its against test11, you need to turn CONFIG_SMT
>>on), although if Ingo's patch doesn't help much, mine probably won't
>>either.
>>
>
>Hi Nick,
>
>Went ahead and tried your patch, but it looks like something's wrong.  If
>this helps any:
>

Doh. OK, did you manage to capture anything above this?

>
>Process postmaster (pid: 1086, threadinfo=f5c40000 task=f5c586b0)
>Stack: f5c5007b 0000007b ffffffff c011f488 00000060 00010046 00000005 c322ccc0 
>       c322c060 00000002 f5c5bdbc f686cb90 f686cb90 f5c41d4c f7f93940 f5ca6080 
>       00000007 00000000 c322ccc0 00006f12 03d99f34 0000033d f5c586b0 f5c41dbc 
>Call Trace:                                                                      [<c011f488>] schedule+0x380/0x705
> [<c01ff412>] sys_semtimedop+0x460/0x530
> [<c011e5bb>] find_busiest_group+0x2bc/0x2e3
> [<c02c69ea>] p4_check_ctrs+0xab/0x11b      
> [<c011e5bb>] find_busiest_group+0x2bc/0x2e3
> [<c02c5a5d>] nmi_callback+0x25/0x29        
> [<c014218d>] buffered_rmqueue+0xea/0x199
> [<c010b8f5>] nmi_stack_correct+0x1e/0x2e
> [<c01422eb>] __alloc_pages+0xaf/0x334   
> [<c014007b>] generic_file_aio_write_nolock+0x298/0xa9e
> [<c014d0c2>] do_anonymous_page+0x16a/0x28b            
> [<c014d80b>] handle_mm_fault+0x101/0x1ad  
> [<c011c4f5>] do_page_fault+0x2fa/0x4fc  
> [<c011eb6d>] rebalance_tick+0x8a/0x91 
> [<c02c4368>] oprofile_add_sample+0x9b/0x117
> [<c02c69ea>] p4_check_ctrs+0xab/0x11b      
> [<c0111ec4>] sys_ipc+0x61/0x2ae      
> [<c02c5a5d>] nmi_callback+0x25/0x29
> [<c010c839>] do_nmi+0x39/0x5a      
> [<c010ad4d>] sysenter_past_esp+0x52/0x71
>                                         
>Code:  Bad EIP value.
>
>
>
>  
>