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6248f45674
Single-stepping through head_64.S made me look at the fixmap page PTEs fixup loop: So we're going through the whole level2_fixmap_pgt 4K page, looking at whether PAGE_PRESENT is set in those PTEs and add the delta between where we're compiled to run and where we actually end up running. However, if that delta is 0 (most cases) we go through all those 512 PTEs for no reason at all. Oh well, we add 0 but that's no reason to me. Skipping that useless fixup gives us a boot speedup of 0.004 seconds in my guest. Not a lot but considering how cheap it is, I'll take it. Here is the printk time difference: before: ... [ 0.000000] tsc: Marking TSC unstable due to TSCs unsynchronized [ 0.013590] Calibrating delay loop (skipped), value calculated using timer frequency.. 8027.17 BogoMIPS (lpj=16054348) [ 0.017094] pid_max: default: 32768 minimum: 301 ... after: ... [ 0.000000] tsc: Marking TSC unstable due to TSCs unsynchronized [ 0.009587] Calibrating delay loop (skipped), value calculated using timer frequency.. 8026.86 BogoMIPS (lpj=16053724) [ 0.013090] pid_max: default: 32768 minimum: 301 ... For the other two changes converting naked numbers to defines: # arch/x86/kernel/head_64.o: text data bss dec hex filename 1124 290864 4096 296084 48494 head_64.o.before 1124 290864 4096 296084 48494 head_64.o.after md5: 87086e202588939296f66e892414ffe2 head_64.o.before.asm 87086e202588939296f66e892414ffe2 head_64.o.after.asm Signed-off-by: Borislav Petkov <bp@suse.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20161125111448.23623-1-bp@alien8.de Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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| boot | ||
| configs | ||
| crypto | ||
| entry | ||
| events | ||
| ia32 | ||
| include | ||
| kernel | ||
| kvm | ||
| lguest | ||
| lib | ||
| math-emu | ||
| mm | ||
| net | ||
| oprofile | ||
| pci | ||
| platform | ||
| power | ||
| purgatory | ||
| ras | ||
| realmode | ||
| tools | ||
| um | ||
| video | ||
| xen | ||
| .gitignore | ||
| Kbuild | ||
| Kconfig | ||
| Kconfig.cpu | ||
| Kconfig.debug | ||
| Makefile | ||
| Makefile.um | ||
| Makefile_32.cpu | ||