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ccachinglinux-kernelpowerpc

Flush CPU data caches in Linux kernel module

I have a Linux kernel module which calculates network packet statistics among several CPUs (in kernel address space). Periodically I clear the corresponding memory chunk and strongly need this action to take immediate effect for all CPUs, otherwise it will distort the subsequent statistics values. My target CPU is a Power PC, so its cache coherency is very relaxed. Thus I need to manually flush data caches of all CPUs just after zeroing the memory.

So what should I place just after my clearing procedure:

memset(ptr, 0, size);
// what's going here?
Solution

  • After some reflection I realised that the problem here is not really linked to data cache flushing. Actually I try to avoid a banal race condition (the first cpu clears value while the second increments it). In my case it's too expensive to protect data by mutex, so it's worth using atomic flag to notify the owning CPU to clear the values by itself.