I presume this is the same system using both versions of cpuminer-opt.
I've reviewed the changes I made for 64 CPU support and they should only have an effect when
there are more than 64 vcores. It's as simple as if num_cpus > 64 do something different else
do as usual.
I can find no reason why it behaves differently or why it maxes at 32.
Test both versions with -D, the debug output may provide a clue.
Edit: Also is there anything unusual about that system? Any virtualization or NUMA?
Tried 3.7.5 vs 3.7.6 - 3.7.5 runs on all CPUs, 3.7.6 only works on 32 CPUs and gives lower hash rates.
Both versions start the same number of threads:
# ps -eLf|grep -c cpuminer
52
Both versions start in the same way with -D:
[2017-12-16 01:03:56] Starting Stratum on stratum+tcp://ip:port
[2017-12-16 01:03:56] Binding thread 0 to cpu 0 (mask 1)
[2017-12-16 01:03:56] Binding thread 1 to cpu 1 (mask 2)
[2017-12-16 01:03:56] Binding thread 2 to cpu 2 (mask 4)
[2017-12-16 01:03:56] Binding thread 3 to cpu 3 (mask 8)
[2017-12-16 01:03:56] Binding thread 4 to cpu 4 (mask 10)
[2017-12-16 01:03:56] Binding thread 5 to cpu 5 (mask 20)
[2017-12-16 01:03:56] Binding thread 6 to cpu 6 (mask 40)
[2017-12-16 01:03:56] Binding thread 7 to cpu 7 (mask 80)
[2017-12-16 01:03:56] Binding thread 8 to cpu 8 (mask 100)
[2017-12-16 01:03:56] Binding thread 9 to cpu 9 (mask 200)
[2017-12-16 01:03:56] Binding thread 10 to cpu 10 (mask 400)
[2017-12-16 01:03:56] Binding thread 11 to cpu 11 (mask 800)
[2017-12-16 01:03:56] Binding thread 12 to cpu 12 (mask 1000)
[2017-12-16 01:03:56] Binding thread 13 to cpu 13 (mask 2000)
[2017-12-16 01:03:56] Binding thread 14 to cpu 14 (mask 4000)
[2017-12-16 01:03:56] Binding thread 15 to cpu 15 (mask 8000)
[2017-12-16 01:03:56] Binding thread 16 to cpu 16 (mask 10000)
[2017-12-16 01:03:56] Binding thread 17 to cpu 17 (mask 20000)
[2017-12-16 01:03:56] Binding thread 18 to cpu 18 (mask 40000)
[2017-12-16 01:03:56] Binding thread 19 to cpu 19 (mask 80000)
[2017-12-16 01:03:56] Binding thread 20 to cpu 20 (mask 100000)
[2017-12-16 01:03:56] Binding thread 21 to cpu 21 (mask 200000)
[2017-12-16 01:03:56] Binding thread 22 to cpu 22 (mask 400000)
[2017-12-16 01:03:56] Binding thread 23 to cpu 23 (mask 800000)
[2017-12-16 01:03:56] Binding thread 24 to cpu 24 (mask 1000000)
[2017-12-16 01:03:56] Binding thread 25 to cpu 25 (mask 2000000)
[2017-12-16 01:03:56] Binding thread 26 to cpu 26 (mask 4000000)
[2017-12-16 01:03:56] Binding thread 27 to cpu 27 (mask 8000000)
[2017-12-16 01:03:56] Binding thread 28 to cpu 28 (mask 10000000)
[2017-12-16 01:03:56] Binding thread 29 to cpu 29 (mask 20000000)
[2017-12-16 01:03:56] Binding thread 30 to cpu 30 (mask 40000000)
[2017-12-16 01:03:56] Binding thread 31 to cpu 31 (mask 80000000)
[2017-12-16 01:03:56] Binding thread 32 to cpu 32 (mask 1)
[2017-12-16 01:03:56] Binding thread 33 to cpu 33 (mask 2)
[2017-12-16 01:03:56] Binding thread 34 to cpu 34 (mask 4)
[2017-12-16 01:03:56] Binding thread 35 to cpu 35 (mask 8)
[2017-12-16 01:03:56] Binding thread 36 to cpu 36 (mask 10)
[2017-12-16 01:03:56] Binding thread 37 to cpu 37 (mask 20)
[2017-12-16 01:03:56] Binding thread 38 to cpu 38 (mask 40)
[2017-12-16 01:03:56] Binding thread 39 to cpu 39 (mask 80)
[2017-12-16 01:03:56] Binding thread 40 to cpu 40 (mask 100)
[2017-12-16 01:03:56] Binding thread 41 to cpu 41 (mask 200)
[2017-12-16 01:03:56] Binding thread 42 to cpu 42 (mask 400)
[2017-12-16 01:03:56] Binding thread 43 to cpu 43 (mask 800)
[2017-12-16 01:03:56] Binding thread 44 to cpu 44 (mask 1000)
[2017-12-16 01:03:56] Binding thread 45 to cpu 45 (mask 2000)
[2017-12-16 01:03:56] Binding thread 46 to cpu 46 (mask 4000)
[2017-12-16 01:03:56] 48 miner threads started, using 'lyra2z' algorithm.
[2017-12-16 01:03:56] Binding thread 47 to cpu 47 (mask 8000)
[2017-12-16 01:03:57] Stratum session id: deadbeefcafebabef76c160000000000
[2017-12-16 01:03:57] Stratum difficulty set to 10
[2017-12-16 01:03:58] Stratum difficulty set to 5
[2017-12-16 01:03:58] DEBUG: job_id='1e40' extranonce2=00000000 ntime=5a3470e6
[2017-12-16 01:03:58] Stratum difficulty set to 10 (0.03906)
(...)
Edit: Also is there anything unusual about that system? Any virtualization or NUMA?
There isn't anything unusual about this system, no virtualization, no multiple sockets etc.