Re: [PATCH v2 2/2] HWRNG: thunderx: Add Cavium HWRNG driver for ThunderX SoC.

From: David Daney
Date: Wed Aug 24 2016 - 19:07:56 EST

On 08/23/2016 10:46 PM, Corentin LABBE wrote:

+/* Read data from the RNG unit */
+static int cavium_rng_read(struct hwrng *rng, void *dat, size_t max, bool wait)
+ struct cavium_rng *p = container_of(rng, struct cavium_rng, ops);
+ unsigned int size = max;
+ while (size >= 8) {
+ *((u64 *)dat) = readq(p->result);
+ size -= 8;
+ dat += 8;
+ }

I think you could use readsq()
This will increase throughput

If you look at the implementation of readsq(), you will see that it is a similar loop. Since the overhead is primarily I/O latency from the RNG hardware, the throughput cannot really be changed with micro optimizations to this simple loop.

Also, on big-endian kernels, it appears that a loop of readq() and readsq() will give different results as readq will byte swap the result and readsq does not. Since this is a RNG, the byte swapping is not important, but it is a difference.

Because of this, I think it should be acceptable to stick with the loop we currently have.

If the hwrng maintainers want to change the loop, to a readsq(), we might investigate this more.

David Daney