Thank you for your research on and posting on it, when I first encountered this issue I saw your posting/research on this issue, this gave me a great insight.
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. could you guide me how to set, the parameter current_clocksource to TSC, Thanks Deepak On Thu, Mar 24, 2011 at 5:07 AM, Achilleas Mantzios < ach...@matrix.gatewaynet.com> wrote: > Στις Thursday 24 March 2011 13:39:19 ο/η Marti Raudsepp έγραψε: > > On Thu, Mar 24, 2011 at 11:11, Achilleas Mantzios > > <ach...@matrix.gatewaynet.com> wrote: > > > My problem had to do with the speed of gettimeofday. You might want to > do some special setting regarding > > > your box's way of reading time for the hw clock. > > > > Just for extra info, on x86, TSC is usually the "fast" timeofday > > implementation. On recent CPUs in single-socket configurations, TSC > > should always be available, regardless of any power management. I > > don't know about multi-socket. If you want to know whether your kernel > > is using tsc, run: > > > > That's what i am experiencing as well, in two of my FreeBSD boxes > (work/home) i get: > > phenom ii X4 : > ========== > % sysctl -a | grep -i timecounter > kern.timecounter.tick: 1 > kern.timecounter.choice: TSC(-100) HPET(900) ACPI-fast(1000) i8254(0) > dummy(-1000000) > kern.timecounter.hardware: TSC > kern.timecounter.stepwarnings: 0 > kern.timecounter.tc.i8254.mask: 65535 > kern.timecounter.tc.i8254.counter: 1960 > kern.timecounter.tc.i8254.frequency: 1193182 > kern.timecounter.tc.i8254.quality: 0 > kern.timecounter.tc.ACPI-fast.mask: 4294967295 > kern.timecounter.tc.ACPI-fast.counter: 3642319843 > kern.timecounter.tc.ACPI-fast.frequency: 3579545 > kern.timecounter.tc.ACPI-fast.quality: 1000 > kern.timecounter.tc.HPET.mask: 4294967295 > kern.timecounter.tc.HPET.counter: 1160619197 > kern.timecounter.tc.HPET.frequency: 14318180 > kern.timecounter.tc.HPET.quality: 900 > kern.timecounter.tc.TSC.mask: 4294967295 > kern.timecounter.tc.TSC.counter: 2788277817 > kern.timecounter.tc.TSC.frequency: 3400155810 > kern.timecounter.tc.TSC.quality: -100 > kern.timecounter.smp_tsc: 0 > kern.timecounter.invariant_tsc: 1 > > Pentium 4 > ====== > % sysctl -a | grep -i timecounter > kern.timecounter.tick: 1 > kern.timecounter.choice: TSC(800) ACPI-fast(1000) i8254(0) dummy(-1000000) > kern.timecounter.hardware: ACPI-fast > kern.timecounter.stepwarnings: 0 > kern.timecounter.tc.i8254.mask: 65535 > kern.timecounter.tc.i8254.counter: 13682 > kern.timecounter.tc.i8254.frequency: 1193182 > kern.timecounter.tc.i8254.quality: 0 > kern.timecounter.tc.ACPI-fast.mask: 16777215 > kern.timecounter.tc.ACPI-fast.counter: 6708142 > kern.timecounter.tc.ACPI-fast.frequency: 3579545 > kern.timecounter.tc.ACPI-fast.quality: 1000 > kern.timecounter.tc.TSC.mask: 4294967295 > kern.timecounter.tc.TSC.counter: 3109326068 > kern.timecounter.tc.TSC.frequency: 2663194296 > kern.timecounter.tc.TSC.quality: 800 > kern.timecounter.smp_tsc: 0 > kern.timecounter.invariant_tsc: 0 > > TSC, it seems, outperform the rest of clocks in terms of frequency. > > > cat /sys/devices/system/clocksource/clocksource0/current_clocksource > > > > On older CPUs, you often had to disable some sort of power management > > in order to get a stable TSC -- the "ondemand" scaling governor is the > > top suspect. Disabling this is distro-specific. You have to reboot to > > get the kernel to re-test TSC. Unfortunately disabling power > > management later at boot doesn't help you, you have to prevent it from > > activating at all. > > > > For debugging, grepping dmesg for tsc or clocksource is often helpful. > > On machines with unstable TSC you'll see output like this: > > > > [ 0.000000] Fast TSC calibration using PIT > > [ 0.164068] checking TSC synchronization [CPU#0 -> CPU#1]: passed. > > [ 0.196730] Switching to clocksource tsc > > [ 0.261347] Marking TSC unstable due to TSC halts in idle > > [ 0.261536] Switching to clocksource acpi_pm > > > > If you just want to get repeatable timings, you can force both > > machines to use the hpet clocksource: > > echo hpet > > /sys/devices/system/clocksource/clocksource0/current_clocksource > > > > Marti > > > > > > -- > Achilleas Mantzios > > -- > Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance >
