On Tue, 29 Jan 2013, Joonsoo Kim wrote: > On Mon, Jan 28, 2013 at 01:04:24PM -0500, Nicolas Pitre wrote: > > On Mon, 28 Jan 2013, Will Deacon wrote: > > > > > Hello, > > > > > > On Thu, Jan 24, 2013 at 01:28:51AM +0000, Joonsoo Kim wrote: > > > > In current implementation, we used ARM-specific flag, that is, > > > > VM_ARM_STATIC_MAPPING, for distinguishing ARM specific static mapped > > > > area. > > > > The purpose of static mapped area is to re-use static mapped area when > > > > entire physical address range of the ioremap request can be covered > > > > by this area. > > > > > > > > This implementation causes needless overhead for some cases. > > > > For example, assume that there is only one static mapped area and > > > > vmlist has 300 areas. Every time we call ioremap, we check 300 areas for > > > > deciding whether it is matched or not. Moreover, even if there is > > > > no static mapped area and vmlist has 300 areas, every time we call > > > > ioremap, we check 300 areas in now. > > > > > > > > If we construct a extra list for static mapped area, we can eliminate > > > > above mentioned overhead. > > > > With a extra list, if there is one static mapped area, > > > > we just check only one area and proceed next operation quickly. > > > > > > > > In fact, it is not a critical problem, because ioremap is not frequently > > > > used. But reducing overhead is better idea. > > > > > > > > Another reason for doing this work is for removing vm_struct list > > > > management, > > > > entirely. For more information, look at the following link. > > > > http://lkml.org/lkml/2012/12/6/184 > > > > > > First patch looks good (removing the unused vmregion stuff) but I'm not so > > > sure about the rest of it. If you really care about ioremap performance, > > > perhaps it would be better to have a container struct around the vm_struct > > > for static mappings and then stick them in an augmented rbtree so you can > > > efficiently find the mapping encompassing a particular physical address? > > > > How can ioremap performance be a problem is the question I had since the > > beginning. > > > > Firstly, ioremap is _not_ meant to be used in performance critical > > paths. > > > > Secondly, there shouldn't be _that_ many entries on the vmlist such as > > 300. That sounds a bit excessive. > > > > So please, can we discuss the reasons that motivated those patches in > > the first place? Maybe that's where the actual problem is. > > Hello, Wiil and Nicolas. > First of all, thanks for reviewing. > > There is another reason for doing this work. > As mentioned above, I try to remove list management for vm_struct(vmlist), > entirely. For that purpose, removing architecture dependency against vmlist > is needed. Below link is for my RFC patch trying to remove list management > for vm_struct. > > http://lkml.org/lkml/2012/12/6/184
OK, I get it now. I do have comments on your patches. I'll provide them as a reply to them. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
