[Dovecot] Ongoing performance issues with 2.0.x
Ralf.Hildebrandt at charite.de
Mon Nov 8 20:44:52 EET 2010
* Stan Hoeppner <stan at hardwarefreak.com>:
> Does this machine have more than 4GB of RAM? You do realize that merely
> utilizing PAE will cause an increase in context switching, whether on
> bare medal or in a VM guest. It will probably actually be much higher
> with a VM guest running a PAE kernel. Also, please tell me the ESX
> kernel you're running is native 64 bit, not 32 bit. If the VMWare
> kernel itself is doing PAE, as well as the guest Linux kernel, this may
> fully explain the performance disaster you have on your hands, if it is
> indeed due to context switching.
It sure work with 1.2.x now, so that's not really the problem
> The bigger question is, why does this problem surface so readily while
> running Dovecot 2.0.x and not while running Dovecot 1.2.x?
> Is 1.2.x merely tickling the dragon's chin, whereas 2.0.x is sticking
> it's head into the dragon's mouth?
I'd say the difference between 1.2 and 2.0 is so dramatic that it's
probably something else.
> This very well may be the case. You need to also look at the CONFIG_HZ=
> value of the Linux kernel of the guest. If it's a tickless kernel you
> should be fine. If tickless, IIRC, you should see CONFIG_NO_HZ=y.
# fgrep HZ config-2.6.32-23-generic-pae
# CONFIG_HZ_100 is not set
# CONFIG_HZ_300 is not set
# CONFIG_HZ_1000 is not set
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