From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Holt Date: Tue, 24 Jan 2006 12:10:52 +0000 Subject: Re: [PATCH] SN2 user-MMIO CPU migration Message-Id: <20060124121052.GC5334@lnx-holt.americas.sgi.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 On Mon, Jan 23, 2006 at 11:04:21PM -0800, Grant Grundler wrote: > On Tue, Jan 24, 2006 at 12:30:42AM -0600, Brent Casavant wrote: > > On Mon, 23 Jan 2006, Grant Grundler wrote: > > > Would an app first need to mmap an uncached address? > > > Or some other obvious "marker" that might warn the kernel? > > > > I'm not sure an uncached address would be appropriate, as I > > believe there are other non-IO uncached mappings which can > > be performed (whatever the fetchop stuff morphed into, for > > example -- I can't remember what its called now). > > OK - just not many user space programs map uncache IO space. The mspec driver does. It has not gotten into the mainline kernel yet, but we continue to build an add-on module for the necessary releases. To prevent this out of order write from happening on those machines, we require the process to be pinned to a single cpu. For MPI, this is a normal way to operate for other reasons as well. Brent, if you find a way to prevent this out-of-order write, please remind me to include it in the mspec driver. Thanks, Robin