On Tue, Nov 8, 2022 at 8:51 AM Edgecombe, Rick P <rick.p.edgecombe@xxxxxxxxx> wrote: > > On Tue, 2022-11-08 at 13:27 +0200, Mike Rapoport wrote: > > > Based on our experiments [5], we measured 0.5% performance > > > improvement > > > from bpf_prog_pack. This patchset further boosts the improvement to > > > 0.7%. > > > The difference is because bpf_prog_pack uses 512x 4kB pages instead > > > of > > > 1x 2MB page, bpf_prog_pack as-is doesn't resolve #2 above. > > > > > > This patchset replaces bpf_prog_pack with a better API and makes it > > > available for other dynamic kernel text, such as modules, ftrace, > > > kprobe. > > > > > > The proposed execmem_alloc() looks to me very much tailored for x86 > > to be > > used as a replacement for module_alloc(). Some architectures have > > module_alloc() that is quite different from the default or x86 > > version, so > > I'd expect at least some explanation how modules etc can use execmem_ > > APIs > > without breaking !x86 architectures. > > I think this is fair, but I think we should ask ask ourselves - how > much should we do in one step? > > For non-text_poke() architectures, the way you can make it work is have > the API look like: > execmem_alloc() <- Does the allocation, but necessarily usable yet > execmem_write() <- Loads the mapping, doesn't work after finish() > execmem_finish() <- Makes the mapping live (loaded, executable, ready) > > So for text_poke(): > execmem_alloc() <- reserves the mapping > execmem_write() <- text_pokes() to the mapping > execmem_finish() <- does nothing > > And non-text_poke(): > execmem_alloc() <- Allocates a regular RW vmalloc allocation > execmem_write() <- Writes normally to it > execmem_finish() <- does set_memory_ro()/set_memory_x() on it Yeah, some fallback mechanism like this is missing in current version. It is not a problem for BPF programs, as we call it from arch code. But we do need better APIs for modules. Thanks, Song > > Non-text_poke() only gets the benefits of centralized logic, but the > interface works for both. This is pretty much what the perm_alloc() RFC > did to make it work with other arch's and modules. But to fit with the > existing modules code (which is actually spread all over) and also > handle RO sections, it also needed some additional bells and whistles. > > So the question I'm trying to ask is, how much should we target for the > next step? I first thought that this functionality was so intertwined, > it would be too hard to do iteratively. So if we want to try > iteratively, I'm ok if it doesn't solve everything. > >
