QEMU 7.2-rc1 Released - TCG For AVX/AVX2, Massive 9pfs Performance Improvement

Written by Michael Larabel in Virtualization on 16 November 2022 at 03:00 PM EST. 11 Comments
QEMU 7.2 is gearing up for release in December as the next feature release to this widely-used processor emulator by the Linux virtualization stack. QEMU 7.2-rc1 is available for testing with a number of new features and improvements coming in this release.

QEMU 7.2 should be out by mid-December depending upon how many weekly release candidates end up being warranted. Among the changes coming with QEMU 7.2 include:

- QEMU for x86/x86_64 now supports the CORE_THREAD_COUNT MSR. There is also support for passing a random seed to the Linux kernel when booted using the "-kernel" argument.

- The Tiny Code Generator (TCG) has performance improvements in full system emulation mode, fixes for its SSE implementation, and TCG now supports AVX / AVX2 / F16C / FMA3 / VAES instructions.

- QEMU with 9pfs has a "massive general performance improvement" as much as 6~12x better performance. This massive speed-up in the QEMU 9pfs code comes from making use of a GHashTable for the FID table. With the change by Linus Heckemann, "This change uses a hashtable for this instead, significantly improving
the performance of the 9p filesystem. The runtime of NixOS's simple installer test, which copies ~122k files totalling ~1.8GiB from 9p, decreased by a factor of about 10.

- QEMU's RISC-V code now supports Zihintpause, disas support for vector instructions, promoting zmmul out of being experimental, improvements to the debugger spec, and other RISC-V improvements.

- QEMU for s390x now supports SHA-512 via KIMD/KLMD instructions, fixed emulation of LZRF and VISTR instructions, and implementing other features.

- Stability improvements to the QEMU OpenRISC code as well as performance improvements.

- QEMU on Arm now supports emulating Enhanced Translation Synchronization, PMU Extensions v3.5, guest translation granule size, HAFDBS, and E0PD. The Arm Cortex-A35 CPU type can also now be emulated.

- Big endian 32-bit MIPS hosts have been deprecated.

More details on all of the changes slated for QEMU 7.2 via the work-in-progress release notes on the QEMU Wiki.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via MichaelLarabel.com.

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