From: Reshetova, Elena
> Sent: 03 May 2019 17:17
...
> rdrand (calling every 8 syscalls): Simple syscall: 0.0795 microseconds
You could try something like:
u64 rand_val = cpu_var->syscall_rand
while (unlikely(rand_val == 0))
rand_val = rdrand64();
stack_offset = rand_val & 0xff;
rand_val >>= 6;
if (likely(rand_val >= 4))
cpu_var->syscall_rand = rand_val;
else
cpu_var->syscall_rand = rdrand64();
return stack_offset;
That gives you 10 system calls per rdrand instruction
and mostly takes the latency out of line.
David
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