Re: Low perf with smp

Thanks a lot Lucas.
What's sound so strange to me is that  there we so much difference 30sec=> 
54 sec simply by activating smp in kernel.
But I will search on this way and see if it don't come from mysql.

I will send  you issue.

Eric.






----- Original Message ----- 
From: "Lucas Holt" <[email protected]>
To: "Eric" <[email protected]>
Cc: <[email protected]>
Sent: Friday, March 31, 2006 2:00 AM
Subject: Re: Low perf with smp


> As i recall, mysql under FreeBSD 4.x used a userland threads  library. 
> That means its only capable of being scheduled on 1 cpu at  a time and 
> each thread is part of one process.  I don't think SMP  will help you much 
> in this case.  There have been a number of threads  on some of the lists 
> (hacker@ ?) in the last few months about MySQL  performance indicating it 
> might have something to do with the timer,  etc.  It might be worth 
> looking into.
>
> Some people have stated that FreeBSD 5 and 6 are slower with disk io, 
> etc.  Plus you've got a raid 1 mirror which will slow down writes.   6.1 
> also has a reported issue with the 4bsd scheduler performance.  Maybe 
> thats part of the problem?
>
> On Mar 30, 2006, at 11:41 AM, Eric wrote:
>
>> Mail NETvigieHi all,
>>
>> I buy a new DELL PowerEdge 1850 with Bi-Xeon 2.8GHZ/2*2MB Dual Core 
>> 800FSB processor, 2Go DDR2 RAM, PERC4di RAID controller with 2 SCSI  U320 
>> 15.000tpm 36Go hdd on RAID1.
>>
>> I install on it Freebsd 6.0, apache 2.2.0 and mysql 4.1.18 and  compare 
>> performance with :
>> OLD PowerEDge with only simple Bi-Xeon 3.0 GHZ and freebsd 4.11.
>>
>> The test is simple mysql query done by php script.
>>
>> Result is that test is two time slower with freebsd 6.0 and dual- core 
>> than with old server.
>> I try with and without smp and  threaded kernel and results are same.
>> I came back to Generic kernel to see if it come from my kernel 
>> configuration but result was same.
>>
>> I then though it come from server and try to upgrade an other one  and 
>> have same result.
>> I then think it come from 6.0 and try with 6.1 beta4 and see same  result
>> I then downgrad to 4.11 without smp and then find good perfs.
>> So I just add to 4.11 generic kernel :
>> options         SMP                     # Symmetric MultiProcessor 
>> Kernel
>> options         APIC_IO                 # Symmetric (APIC) I/O
>>
>> And then perf go back down from 30secondes to 54 sec.
>> I search a lot on internet and try with this : sysctl 
>> machdep.cpu_idle_hlt=0
>> But result is same.
>>
>> When doing whith smp top it's just as mysql have to wait to have  cpu. 
>> During 10,20 sec it just go to 2,4% then grow. Without smp it  grow very 
>> quickly.
>>
>> Does anyone know what's go wrong and what do I have to do to have  same 
>> perf with smp than without?
>>
>> Thanks,
>>
>> Eric.
>>
>>
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>
>
> Lucas Holt
> [email protected]
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