Messages in this thread | | | Date | Wed, 24 Aug 2016 16:07:25 -0700 | From | David Daney <> | Subject | Re: [PATCH v2 2/2] HWRNG: thunderx: Add Cavium HWRNG driver for ThunderX SoC. |
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On 08/23/2016 10:46 PM, Corentin LABBE wrote: > Hello > >> +/* 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.
Thanks, David Daney
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