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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