If it's a HP box you can also turn this off via the bios via your RBSU:
Starting with HP ProLiant G6 servers that utilize Intel® Xeon® processors, setting the HP Power Profile
Option in RBSU to Maximum Performance Mode sets these recommended additional low-latency options
for minimum BIOS latenc
From: pgsql-performance-owner(at)postgresql(dot)org [mailto:pgsql-performance-owner(at)postgresql(dot)org] On Behalf Of Marti Raudsepp
Sent: Friday, March 25, 2011 3:30 AM
Cc: Achilleas Mantzios; pgsql-performance(at)postgresql(dot)org
Subject: Re: [PERFORM] pg9.0.3 explain analyze running very slow compared to a different box with much less configuration
2011/3/25 DM <dm(dot)aeqa(at)gmail(dot)com>:
> gettimeofday() on my new box is slow, after further research we found
> that, when we set ACPI=Off, we got a good clock performance even the
> explain analyze gave approximately gave the right values, but the
> hyperthreading is off.
Disabling ACPI also disables most CPU power management, so that explains why you get a stable TSC that way. But that's not a real fix.
> could you guide me how to set, the parameter current_clocksource to
You can't "set" it, the kernel will automatically choose TSC, if it's stable, at boot time; see messages in dmesg.
A better way to disable power management on CentOS is to disable the 'cpuspeed' service.
Note that this is not necessary for newer CPUs; Intel Nehalem and AMD Phenom series have a stable TSC even with power management enabled.
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