Date: Tue, 13 Sep 2011 10:16:50 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: Brett Glass <brett@lariat.net> Cc: Adam Vande More <amvandemore@gmail.com>, questions@freebsd.org Subject: Re: Negative ping times with FreeBSD 8.1-RELEASE on older Celeron system Message-ID: <20110913151650.GF9801@dan.emsphone.com> In-Reply-To: <201109131021.EAA26090@lariat.net> References: <201109122350.RAA21916@lariat.net> <F06D137D-F364-46B2-9458-6882B543B3A6@mac.com> <201109130443.WAA23650@lariat.net> <CA%2BtpaK2VVdue4MsJpzUxEQABDk1pFVWy_0=CqSEaRifM8CKX5Q@mail.gmail.com> <201109131021.EAA26090@lariat.net>
next in thread | previous in thread | raw e-mail | index | archive | help
In the last episode (Sep 13), Brett Glass said: > Thank you! Since it's tunable at runtime I just tested it, and -- sure > enough -- no negative ping times. > > Ironically, it was the kernel that selected the ACPI timer, scoring it > higher than the timestamp counter as a clock source. Perhaps code should > be added to ensure that the timer is not chosen if it rolls over in less > than a second, since this clearly leads to imprecision and missed > rollovers. > > kern.timecounter.tc.ACPI-safe.mask: 16777215 > kern.timecounter.tc.ACPI-safe.counter: 7967112 > kern.timecounter.tc.ACPI-safe.frequency: 3579545 > kern.timecounter.tc.ACPI-safe.quality: 850 It doesn't roll over in less than a second; it rolls over in 16777215 / 3579545 = 4.6 seconds. Your negative time delta problem isn't due to rollover. -- Dan Nelson dnelson@allantgroup.com
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20110913151650.GF9801>