On Wed, Aug 26, 2009 at 11:06 PM, Pharaoh .<pharaoh137@xxxxxxxxx> wrote: > > > Hi list, > > 1. A cpu can access its own per cpu data atomically but if it has to access > other cpus per cpu data > it might not be atomically accessed. Is this correct? IMO, assuming your per CPU data is something simple like word length (4 byte in x86 32 bit), then yes local access to per CPU data is atomic. But it can not be atomic if it's accessing complex data structure. And IIRC, per CPU API are written to store and retrieve simple type of data. If you're accessing other CPU data, I guess it still might done "atomically" by doing lock (e.g spinlock). But yes, without lock, you have to careful about race condition >If my driver makes > sure that no cpu accesses > other cpu's per cpu data my code can be entirely lockless? Correct? IMO yes. Just make sure you use provided per CPU API. IIRC, when you're accessing per CPU data using the APIs, it will also disable preemption..thus preventing your code to be migrated to other core/CPU. > 2. Can I have a rather complex data structure like a radix tree as a per cpu > data structure? Ehm, I don't think so. Well, theoritically you can but IIRC the kernel doesn't provide such API to store and retrieve such data structure by default. > 3. Is it guaranteed that all the accesses happening to this tree from a cpu > which allocated it are atomic? > I think they are atomic since the per cpu data access functions disable > preemption. > > > My main objective is to have a radix tree which will be accessed on multiple > cores, I want to avoid the > locking overhead of keeping a central lock for accessing this tree. I have > just started investigating the > possibilities. > > > -pharaoh. > -- regards, Mulyadi Santosa Freelance Linux trainer blog: the-hydra.blogspot.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
