From mboxrd@z Thu Jan 1 00:00:00 1970 From: Philippe Gerum In-Reply-To: <49F69924.8070001@domain.hid> References: <49F69924.8070001@domain.hid> Content-Type: text/plain Date: Tue, 28 Apr 2009 12:07:20 +0200 Message-Id: <1240913240.6990.347.camel@domain.hid> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] xenomai 2.5 rc1 timing computations. List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: Xenomai core On Tue, 2009-04-28 at 07:50 +0200, Gilles Chanteperdrix wrote: > Hi, > > currently, the situation is this: > - the timing core uses an approximate value of the cpu frequency (using > xnarch_llmulshft) to do conversions between tsc and ns; > - the APIC timer reprogrammation still uses imuldiv, that is a more > exact cpu frequency, coupled with an approximate APIC frequency > (obtained from ipipe_request_tickdev), to do the conversion between tsc > delays and APIC delays; > - the posix skin uses llimd to do conversions between timespec and > timeval structures and tsc values > - the posix and native skins in user-space still use llimd to do > conversions between ns and tsc (only if using tsc in user-space). > > These are causes of unprecisions, I think we should fix this, though it > is unlikely to be the cause of the high jitters observed by Vikesh with > 2.5-rc1. > Ack, we definitely should. Working on allowing userland to use llmulshift for timing computations for the native skin here, as a first step. For that purpose, xnsysinfo_t has just been extended to carry the pre-scaled values needed for llmulshft. I just don't want to have to issue a syscall for those conversions to take place. > Regards. > -- Philippe.