Messages in this thread | | | Subject | Re: [GIT PATCH] x86,percpu: fix pageattr handling with remap allocator | From | Suresh Siddha <> | Date | Mon, 18 May 2009 14:07:15 -0700 |
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On Mon, 2009-05-18 at 12:41 -0700, H. Peter Anvin wrote: > Suresh Siddha wrote: > > > > Can we don't use PERCPU_DYNAMIC_RESERVE in the first chunk and for > > dynamic per_cpu_ptr's we can use some other offset such as > > per_cpu_ptr_offset() or some such thing? > > > > Then we can separate the static and dynamic chunks. And use large page > > kernel-direct mappings for fast access for critical common things and > > use small page accesses for dynamic and not so common accesses. > > > > Just checking to see if we can reduce the complexity of setting up the > > percpu areas (different versions for embed, non-embed etc) and handling > > all these aliases with simple code, rather than making it complex. > > > > I'm confused what you're suggesting here. The whole point of the percpu > unification work is that we can use %gs:absolute type references to hit > a variable right away. Although in theory we could use both %fs and %gs > for pointers, setting up both would greatly increase the cost of > entering the kernel, especially on 64 bits. > > This means all percpu data has to have a constant (virtual) offset from > the beginning of the static percpu area.
This %gs:absolute type accesses are for static percpu data.
But what I was referring to is the dynamic percpu data(accessed through per_cpu_ptr()). Instead of combining some part of the dynamic percpu data into the static percpu data(first percpu chunk), we can use different chunks for dynamic percpu data and governed by a different per_cpu_dynamic_offset[NR_CPUS] array.
Then we can use large-page kernel direct mappings for static percpu data (or %gs:offset) and small-page vmalloc mappings for dynamic percpu data.
thanks, suresh
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