From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rich Altmaier Date: Thu, 20 Nov 2003 17:25:59 +0000 Subject: Re: [PATCH] - sched_clock() broken for ia64 SN platform Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org Just to add a small note to Jack's comments, the reason for the existance of this "globally synchronized hi-res" counter is exactly for scheduling. On IRIX we use this in the frame-scheduler, to achieve order(tens of microsecond) simultaneous launch of processes on multiple CPUs for hard realtime. The counter is replicated in each memory controller, where the NUMAflex interconnect provides a broadcast clock signal to drive them. It's a fairly cool feature, and the realtime people love it... FYI, Rich Jack Steiner wrote: > > > This is slightly off-topic, but the shared platform counter on the SGI > platform isnt a single counter. The counter is replicated in each chipset > It is synchronized thruout the system so that all cpus will see > the same value - ie., no drift. Reading the counter does not required any > off-node references. There shouldnt be any scaling issues. However, > reading the ITC is faster & preferred if intercpu drift is not an issue. > >