On Monday 19 Sep 2011 12:19:29 AM Dave Hylands wrote:
The way I normally deal with this is to use 2 indicies, a get index and a put index. One of the indicies if only ever written by kernel space, and the other is only ever written by user space.
That is the setup I have now.
You make the circular buffer be a power of 2 in size, and you determine the number of items in the queue by subtracting the get index from the put index.
I am worried about the subtraction. Is it safe to subtract when the put index is in the process of incrementing by the kernel? My queue size is always a power of two and avoid the modulus operation by '&' with (2^n)-1.
If the items in the circular buffer are in cached memory, then I normally try to make each item be an exact multiple of the cache line size. I find using uncached memory is generally better for this type of thing (the accesses are slower, but may be faster after accounting for the cache management).
I am having a chunked buffer. So the queue items are memory chunks ranging from PAGE_SIZE*n to PAGE_SIZE*1. So I have a index to the chunk, index to item inside the chunk for read and write. For the user its invisible and sees it as one big chunk of memory with a read and a write index.