Koji is Fedora's build system:

http://fedora.riscv.rocks/koji/
https://koji.fedoraproject.org/koji/

Doesn't use cross-compilation, and not possible with current design.
We must find a way to run a full build system somehow.

Explanation of primary architecture
               vs. koji-shadow






















## What hardware should we choose for RISC-V as a primary architecture?

* Milk-V Pioneer (SG2042)
* Sophgo 2U server (SG2042)

  - Possible performance and quality issues [unverified]
  - Expensive
  - Likely to end up as e-waste soon.

* SiFive Unmatched

  - Slow
  - Doesn't support any recent extensions, esp. V, H
  - No BMC, but might use BMC-on-PCIe card

* [Mystery manufacturer] future development board (under NDA)

* Single board computers (SBCs)

  - VisionFive2 (StarFive JH7xxx), Lichee Pi 4A, ...
  - Slow
  - Limited memory, cores
  - Reliability issues
  - Upfront & ongoing engineering headaches integrating into a 19" rack

* QEMU

  - Performance numbers below, but not great
  - Really using x86-64 hardware
  - Hardware (x86-64) is well known and easy to manage
  - No "e-waste", servers can be repurposed
  - Supports all the latest extensions
  - Supports any amount of RAM, large numbers of vCPUs
  - We can add new extensions and fix bugs relatively easily






## QEMU performance numbers

(Times in seconds, taken from recent Fedora Koji builds)

               binutils     openssl      python3.12   mingw-gcc

i686           1589         1577         3411         4292

x86-64         1419         1172         2462         1827

aarch64        1573          811 (?)     1845         2521

ppc64le        2165         1291         3073         4388

s390x          2553         1380         1984 (?)     6824




qemu riscv64  [qemu-system-riscv64 16 cores, 16 GB; on AMD Ryzen 9 7950X server]
  (LTO)        4493         3052        14502        12428
                 +217%        +160%       +489%        +580%

  (no LTO)     3267         1351         6353        (failed)
                 +130%        +15%        +158%

VisionFive 2
  (LTO)        7202         8823                     (crashed in LTO step)
                 +408%        +653%

  (no LTO)     3274         2059
                 +130%        +75%



## QEMU observations

"TCG" is the name for QEMU's software emulation, eg. RISC-V fully
emulated guest on x86-64 host.

Works using Translation Blocks (TBs) which translate basic blocks of
guest code.

Well understood (by me), easy to fix simpler issues.

 - I posted a patch yesterday which gets ~ +6% performance gain

A few tips to make TCG run (a bit) fast(er):

 - Compile with -march=native (+4%)

 - Profile with perf

 - Don't overprovision host CPUs

    * However pinning vCPUs to pCPUs didn't really help

 - Give it plenty of guest & host RAM

    * Measured memory overhead on host is up to 40% after running
      for some time

    * Host TBs track guest page cache; as long as a translated
      executable remains in the guest page cache, it will not be
      retranslated

 - Don't restart the VM

 - Software TLB

 - Fast vs slow jumps