From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [ofa-general] Re: [GIT PULL] please pull ummunotify Date: Tue, 13 Oct 2009 10:27:25 -0600 Message-ID: <20091013162725.GL18578@obsidianresearch.com> References: <20090929171332.GD14405@elf.ucw.cz> <20090930094456.GD24621@elte.hu> <20090930160232.GZ22310@obsidianresearch.com> <20091012181944.GF17138@elte.hu> <20091012193048.GA20313@obsidianresearch.com> <20091012202046.GA7648@elte.hu> <20091013040515.GI18578@obsidianresearch.com> <20091013064006.GC9470@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20091013064006.GC9470-X9Un+BFzKDI@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ingo Molnar Cc: Pavel Machek , Roland Dreier , Peter Zijlstra , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Paul Mackerras , Anton Blanchard , general-ZwoEplunGu1OwGhvXhtEPSCwEArCW2h5@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, Jeff Squyres List-Id: linux-rdma@vger.kernel.org On Tue, Oct 13, 2009 at 08:40:06AM +0200, Ingo Molnar wrote: > > * Jason Gunthorpe wrote: > > > On Mon, Oct 12, 2009 at 10:20:46PM +0200, Ingo Molnar wrote: > > > It might be more acceptable because the flag-hint mechanism can at most > > > cause over-flushing - while with perf events we might miss to invalidate > > > a range altogether. > > > > Right. Overflushing is not important, but missing an event entirely is > > not recoverable (at least within the current kernel APIs). > > So if we detect event loss in the perf event case (should not happen > with sufficient buffering but it is a possibility the code should be > prepared for) then we can just flush the [0,-1ULL] range, right? No, the reason overflushing within a registration is OK is because of how the MPI APIs are defined and typically used. The map and registration window will typically be 1:1 ie you malloc something and then register it. It is an error to register beyond your malloced space. So, in truth, the hint stuff isn't really essential for MPI. flushing all ranges would result in data loss since ranges may be in use at the time, and 'flush' is actually unregister/reregister - the hardware cannot do in place atomic modify. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html