Intel's new Chimera: Alder Lake

[andreas]

With 8000 8-byte NOPS, the bottleneck are not the decoders, but instruction cache misses. You can see this by looking at the L2_RQSTS.CODE_RD_HIT counter (24.C4):

Code: Select all

sudo ./nanoBench.sh -f -conf configs/cfg_AlderLakeP_all.txt -cpu 0 -basic -unroll 1000 -loop 1000 -asm "|8|8|8|8|8|8|8|8" | grep -v 0.00

RDTSC: 3.01
Instructions retired: 8.00
Core cycles: 4.00
Reference cycles: 3.01
L2_RQSTS.CODE_RD_HIT: 1.00
L2_RQSTS.ALL_CODE_RD: 1.00
L2_REQUEST.ALL: 1.00
L2_REQUEST.ALL: 1.00
...

[agner]

We have now made some more tests on the P core after fixing the problem with overheating the CPU. The results are more stable now and basically confirming what Andreas wrote:

• The decoders can handle up to 6 µops per clock
• Simple integer instructions have a maximum throughput of 5 instructions per clock
• Integer additions with a small immediate constant have latencies near zero.
• Floating point addition has a latency of 2 clock cycles in chains of similar instructions, otherwise the latency is 3.
• Cache read throughput: 3 reads per clock with sizes ≤ 256 bits. 2 reads/clock with 512 bits
• Cache write throughput: 2 writes per clock with sizes ≤ 256 bits. 1 write/clock with 512 bits
• Mixed read/write throughput: 3 reads and 1 write per clock with sizes ≤ 128 bits

[alfred0809]

I have tested an Alder Lake, but I have not been able to get access to a setup that makes it possible to enable the AVX512 instructions. The performance of the P cores is improved somewhat over the Intel Ice Lake. The µop cache can hold 4k µops. The µop cache can deliver a maximum of 6 µops per clock cycle for a single thread

[agner]

The µop cache can hold 4k µops. The µop cache can deliver a maximum of 6 µops per clock cycle for a single thread

This agrees with my measurements.

[agner]

This Reddit post is reporting experiments with how to make sure heavy tasks are running in the P cores
https://www.reddit.com/r/XMG_gg/comment ... ores_when/.

I still think it is unreasonable to expect ordinary computer users to attend to processor-specific performance tuning details. Intel's confusing product names makes it difficult to even know what microarchitecture your computer is based on.