Date: Tue, 29 Nov 2011 13:25:53 -0600 From: Adam Vande More <amvandemore@gmail.com> To: Ireneusz Pluta <ipluta@wp.pl> Cc: freebsd-questions@freebsd.org Subject: Re: kern.timecounter.hardware change on the fly Message-ID: <CA%2BtpaK1FYa6NyujjNTX5Cxb3XHaWsd4zRrdCP=vgPyUucBQkHg@mail.gmail.com> In-Reply-To: <4ED525B1.3010100@wp.pl> References: <4ED525B1.3010100@wp.pl>
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On Tue, Nov 29, 2011 at 12:34 PM, Ireneusz Pluta <ipluta@wp.pl> wrote: > is it safe to change kern.timecounter.hardware on a busy production system > on the fly? Or I better schedule a downtime to do that? > > It seems I got a bad current selection, somehow, probably as an effect of > leaving /etc/sysctl.conf contents of early experimental setup stage of this > machine. > > $ sysctl -a | grep timecounter > kern.timecounter.tick: 1 > kern.timecounter.choice: TSC(-100) HPET(900) ACPI-fast(1000) i8254(0) > dummy(-1000000) > kern.timecounter.hardware: i8254 > kern.timecounter.stepwarnings: 0 > kern.timecounter.tc.i8254.**mask: 65535 > kern.timecounter.tc.i8254.**counter: 23813 > 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: 4619803 > 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: 1703441786 > kern.timecounter.tc.HPET.**frequency: 14318180 > kern.timecounter.tc.HPET.**quality: 900 > kern.timecounter.tc.TSC.mask: 4294967295 > kern.timecounter.tc.TSC.**counter: 2720513805 > kern.timecounter.tc.TSC.**frequency: 2266656152 > kern.timecounter.tc.TSC.**quality: -100 > kern.timecounter.smp_tsc: 0 > kern.timecounter.invariant_**tsc: 1 > > This setting seems to affect what is generally described here: > http://archives.postgresql.**org/pgsql-admin/2011-01/**msg00059.php<http://archives.postgresql.org/pgsql-admin/2011-01/msg00059.php>and this is the primary reason I want to change. > > Should I switch to HPET or ACPI-fast? > I don't know of any reason it would be unsafe to switch. There have been conflicting reports vs the speed of HPET and ACPI-fast probably at least in part due to hardware differences. You should test each if performance is a concern for you. -- Adam Vande More
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