On Mon, 2007-10-29 at 11:41 -0700, Paul Jackson wrote: > Lee wrote: > > Maybe it's just me, but I think it's pretty presumptuous to think we can > > infer the intent of the application from the nodemask w/o additional > > flags such as Christoph proposed [cpuset relative]--especially for > > subsets of the cpuset. E.g., the application could intend the nodemask > > to specify memories within a certain distance of a physical resource, > > such as where a particular IO adapter or set thereof attach to the > > platform. > > Well, yes, we can't presume to know whether some application can move > or not. > > But our kernel work is not presuming that. > > It's providing mechanisms useful for moving apps. > > The people using this decide what and when and if to move. > > For example, the particular customers (HPC) I focus on for my job don't > move jobs because they don't want to take the transient performance > hit that would come from blowing out all their memory caches. > > I'm guessing that David's situation involves something closer what you > see with a shared web hosting service, running jobs that are very > independent of hardware particulars. > > But in any case, we (the kernel) are just providing the mechanisms. > If they don't fit ones needs, don't use them ;). >
I'm with you on this last point! I was reacting to the notion that we can infer intent from a nodemask and that preserving the cpuset relative numbering after changing cpuset resources or moving tasks preserves that intent--especially if it involves locality and distance considerations. I can envision sets of such transformations on HP platforms where locality and distance would be preserved by preserving cpuset-relative numbering, and many where they would not. I expect you could do the same for SGI platforms. I'm not opposed to what you're trying to do, modulo complexity concerns. And I'm not saying that the complexity is not worth it to customers. But, given that we just "providing the mechanism", I think we need to provide very good documentation on the implications of these mechanism vis a vis whatever characteristics--locality, distance, bandwidth sharing, ...--the application intends when it installs a policy. Like you, no doubt, I'm eyeballs deep in a number of things. At some point, I'll take a cut at enumerating various "intents" that different types of applications might have when using mem policies and cpusets. Others can add to that, or may even beat me to it. We can then evaluate how well these scenarios are served by the current mechanisms and by whatever changes are proposed. I should note that I really like cpusets--i.e., find them useful--and I'm painfully aware of the awkward interactions with mempolicy. On the other hand, I don't want to sacrifice mem policy capabilities to shoe horn them into cpusets. In fact, I want to add additional mechanisms that may also be awkward in cpusets. As you say, "if they don't fit your needs, don't use them." Later, Lee - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
