From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Chen, Kenneth W" Date: Tue, 24 Jan 2006 21:43:57 +0000 Subject: RE: [PATCH] SN2 user-MMIO CPU migration Message-Id: <200601242143.k0OLhug14696@unix-os.sc.intel.com> List-Id: References: <20060118163305.Y42462@chenjesu.americas.sgi.com> In-Reply-To: <20060118163305.Y42462@chenjesu.americas.sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org Brent Casavant wrote on Tuesday, January 24, 2006 1:13 PM > The new patch below implements pretty much exactly that. I'm not > thrilled about carrying around the thread_info.last_cpu field even > on non-SN2, but making the presence/updating of the field conditional > led to huge headaches in the "should we call platform_switch_from" > conditionals/logic. Yeah, I'm not thrilled either. Currently, on context switch kernel doesn't read thread_info.cpu, nor any other neighboring field. With the patch, it needs to do a cacheline read and possibly an update. If unlucky, it might be two cache lines with last_cpu 92 bytes away from thread_info.cpu. Perhaps, last_cpu should be next to cpu field. On the other hand, it may not be too bad because on kernel exit, flags field in thread_info is accessed for TIF_* and if kernel exit path is taken back-to-back with context switch, the net effect maybe small. - Ken