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authorChristian Krinitsin <mail@krinitsin.com>2025-07-03 16:27:09 +0000
committerChristian Krinitsin <mail@krinitsin.com>2025-07-03 16:27:09 +0000
commit4d9e26c0333abd39bdbd039dcdb30ed429c475ba (patch)
tree4010d5fb3e8bc48c110a2c1ff2a16b8648cb86bb /results/classifier/accel-gemma3:12b/tcg/2183
parent5541099586dbd6018574cb44e1934907c121526f (diff)
downloademulator-bug-study-4d9e26c0333abd39bdbd039dcdb30ed429c475ba.tar.gz
emulator-bug-study-4d9e26c0333abd39bdbd039dcdb30ed429c475ba.zip
add gemma accelerator classification results
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+
+aarch-64 emulation much slower since release 8.1.5 (issue also present on 8.2.1)
+Description of problem:
+Since QEMU 8.1.5 our aarch64 based emulation got much slower. We use a linux 5.4 kernel which we cross-compile with the ARM toolchain. Things that are noticable:
+- Boot time got a lot longer
+- All memory accesses seem to take 3x longer (can be verified by e.g. executing below script, address does not matter):
+```
+date
+for i in $(seq 0 1000); do
+    devmem 0x200000000 2>/dev/null
+done
+date
+```
+Steps to reproduce:
+Just boot an ARM based kernel on the virt machine and execute above script.
+Additional information:
+I've tried reproducing the issue on the master branch. There the issue is not present. It only seems to be present on releases 8.1.5 and 8.2.1. 
+
+I've narrowed the problem down to following commit on the 8.2 branch (@bonzini): ef74024b76bf285e247add8538c11cb3c7399a1a accel/tcg: Revert mapping of PCREL translation block to multiple virtual addresses.
+
+Let me know if any other information / tests are required.