On Fri, Mar 12, 2021 at 10:00 PM Borislav Petkov wrote: > > On Fri, Mar 12, 2021 at 12:32:53PM +0100, Peter Zijlstra wrote: > > Since ultimate performance of a 10 year old chip (Intel Sandy Bridge, 2011) is > > simply irrelevant today, remove variable NOPs and use NOPL. > > Just ran them on my SNB box: > > cpu family : 6 > model : 45 > model name : Intel(R) Xeon(R) CPU E5-1620 0 @ 3.60GHz > stepping : 7 > > with the usual perf stat kernel build workload with > CONFIG_DYNAMIC_FTRACE and CONFIG_FUNCTION_TRACER where each function has > a NOP at its beginning when ftrace is disabled (thx Steve). > > ./tools/perf/perf stat --repeat 5 --sync --pre=/root/bin/pre-build-kernel.sh -- make -s -j9 bzImage > > before: tip-master > > Performance counter stats for 'make -s -j9 bzImage' (5 runs): > > 3,213,728.10 msec task-clock # 7.307 CPUs utilized ( +- 0.01% ) > 339,270 context-switches # 0.106 K/sec ( +- 0.09% ) > 31,472 cpu-migrations # 0.010 K/sec ( +- 0.64% ) > 62,070,684 page-faults # 0.019 M/sec ( +- 0.01% ) > 11,498,198,009,323 cycles # 3.578 GHz ( +- 0.01% ) (83.33%) > 8,235,957,366,696 stalled-cycles-frontend # 71.63% frontend cycles idle ( +- 0.01% ) (83.33%) > 5,976,456,688,814 stalled-cycles-backend # 51.98% backend cycles idle ( +- 0.02% ) (66.67%) > 7,553,156,344,376 instructions # 0.66 insn per cycle > # 1.09 stalled cycles per insn ( +- 0.00% ) (83.33%) > 1,635,468,917,524 branches # 508.901 M/sec ( +- 0.00% ) (83.34%) > 51,888,292,932 branch-misses # 3.17% of all branches ( +- 0.02% ) (83.33%) > > 439.809 +- 0.156 seconds time elapsed ( +- 0.04% ) > > > after: tip-master-nops > > Performance counter stats for 'make -s -j9 bzImage' (5 runs): > > 3,217,113.67 msec task-clock # 7.307 CPUs utilized ( +- 0.03% ) > 339,425 context-switches # 0.106 K/sec ( +- 0.20% ) > 31,724 cpu-migrations # 0.010 K/sec ( +- 0.54% ) > 62,027,130 page-faults # 0.019 M/sec ( +- 0.01% ) > 11,508,779,965,901 cycles # 3.577 GHz ( +- 0.03% ) (83.34%) > 8,241,212,210,440 stalled-cycles-frontend # 71.61% frontend cycles idle ( +- 0.04% ) (83.33%) > 5,982,615,533,177 stalled-cycles-backend # 51.98% backend cycles idle ( +- 0.06% ) (66.66%) > 7,546,407,430,314 instructions # 0.66 insn per cycle > # 1.09 stalled cycles per insn ( +- 0.00% ) (83.33%) > 1,634,187,006,479 branches # 507.967 M/sec ( +- 0.00% ) (83.33%) > 51,941,580,371 branch-misses # 3.18% of all branches ( +- 0.01% ) (83.33%) > > 440.266 +- 0.195 seconds time elapsed ( +- 0.04% ) > > > So here's numbers talk, bullshit walks. And with those numbers no > bullshit can remain lingering around anyway. > Here are my numbers. My CPU: cpu family : 6 model : 42 model name : Intel(R) Core(TM) i5-2467M CPU @ 1.60GHz stepping : 7 My base was Linus Git: $ git describe master v5.12-rc2-338-gf78d76e72a46 I used Peter's patchset plus a required pre-patch so that it cleanly applies against Linus Git: x86/jump_label: Mark arguments as const to satisfy asm constraints x86: Remove dynamic NOP selection objtool,x86: Use asm/nops.h My benchmark was to build a Linux-kernel with LLVM/Clang v12.0.0-rc3 on Debian/testing AMD64. Patchset applied for a first build: Performance counter stats for 'make V=1 -j4 LLVM=1 LLVM_IAS=1 PAHOLE=/opt/pahole/bin/pahole LOCALVERSION=-7-amd64-clang12-cfi KBUILD_VERBOSE=1 KBUILD_BUILD_HOST=iniza KBUILD_BUILD_USER=sedat.dilek@gmail.com KBUILD_BUILD_TIMESTAMP=2021-03-12 bindeb-pkg KDEB_PKGVERSION=5.12.0~rc2-7~bullseye+dileks1': 55605704.79 msec task-clock # 3.568 CPUs utilized 8317406 context-switches # 0.150 K/sec 261843 cpu-migrations # 0.005 K/sec 288312867 page-faults # 0.005 M/sec 107642573933061 cycles # 1.936 GHz 82531165255218 stalled-cycles-frontend # 76.67% frontend cycles idle 64932777217096 stalled-cycles-backend # 60.32% backend cycles idle 59591288273663 instructions # 0.55 insn per cycle # 1.38 stalled cycles per insn 10906545460023 branches # 196.141 M/sec 489809039153 branch-misses # 4.49% of all branches 15582.829443660 seconds time elapsed 53102.403996000 seconds user 2547.134916000 seconds sys Building on a kernel where above patchset was applied and booted into and rebuild with the same code-base: Performance counter stats for 'make V=1 -j4 LLVM=1 LLVM_IAS=1 PAHOLE=/opt/pahole/bin/pahole LOCALVERSION=-8-amd64-clang12-cfi KBUILD_VERBOSE=1 KBUILD_BUILD_HOST=iniza KBUILD_BUILD_USER=sedat.dilek@gmail.com KBUILD_BUILD_TIMESTAMP=2021-03-13 bindeb-pkg KDEB_PKGVERSION=5.12.0~rc2-8~bullseye+dileks1': 56976758.12 msec task-clock # 3.589 CPUs utilized 8334519 context-switches # 0.146 K/sec 269340 cpu-migrations # 0.005 K/sec 288451841 page-faults # 0.005 M/sec 110795226760909 cycles # 1.945 GHz 85643743105935 stalled-cycles-frontend # 77.30% frontend cycles idle 68146424096780 stalled-cycles-backend # 61.51% backend cycles idle 59559370217381 instructions # 0.54 insn per cycle # 1.44 stalled cycles per insn 10902087911812 branches # 191.343 M/sec 490447660403 branch-misses # 4.50% of all branches 15875.267204283 seconds time elapsed 54502.552543000 seconds user 2519.914516000 seconds sys Simply comparing the build-times: ~15583 vs. ~15875 means approx. 5mins more build-time. Attached are my linux-configs and above mentioned build-times (in case Gmail has truncated them). - Sedat -