Messages in this thread | | | Date | Fri, 28 Dec 2007 14:05:05 -0800 | From | Mike Travis <> | Subject | Re: [PATCH 05/10] x86_64: Use generic percpu |
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Andi Kleen wrote: > On Friday 28 December 2007 01:10:51 travis@sgi.com wrote: >> x86_64 provides an optimized way to determine the local per cpu area >> offset through the pda and determines the base by accessing a remote >> pda. > > And? The rationale for this patch seems to be incomplete. > > As far as I can figure out you're replacing an optimized percpu > implementation which a dumber generic one. Which needs > at least some description why.
The specific intent for the next wave of changes coming are to reduce the impact of having a large NR_CPUS count on smaller systems and to minimize memory traffic between nodes. This patchset addresses the per_cpu data areas in preparation to cpu_alloc changes to compact the PERCPU area, remove the various per_cpu data offset and pointer arrays, and speed up calculating the per_cpu data offset.
Since those changes have a bigger impact it was felt that we should prepare the groundwork before hand. It also has the benefit of merging one more of the i386 and x86_64 headers.
> If the generic one is now as good or better than the > specific one that might be ok, but that should be somewhere > in the description.
I could gather some performance data, though the effect will be larger as later changes are made.
> Also for such changes .text size comparisons before/after > are a good idea.
x86_64-defconfig:
pre-percpu post-percpu 225 .altinstr_replacemen +0 .altinstr_replacemen 1195 .altinstructions +0 .altinstructions 716104 .bss +0 .bss 58300 .comment +0 .comment 16 .con_initcall.init +0 .con_initcall.init 415816 .data +0 .data 178688 .data.cacheline_alig +0 .data.cacheline_alig 8192 .data.init_task +0 .data.init_task 4096 .data.page_aligned +0 .data.page_aligned 27008 .data.percpu +0 .data.percpu 43904 .data.read_mostly +0 .data.read_mostly 4 .data_nosave +0 .data_nosave 5097 .exit.text +0 .exit.text 138384 .init.data +0 .init.data 133 .init.ramfs +0 .init.ramfs 3192 .init.setup +0 .init.setup 159373 .init.text +3 .init.text 2296 .initcall.init +0 .initcall.init 8 .jiffies +0 .jiffies 4512 .pci_fixup +0 .pci_fixup 1411137 .rodata +8 .rodata 35400 .smp_locks +0 .smp_locks 3629056 .text +48 .text 3368 .vdso +0 .vdso 4 .vgetcpu_mode +0 .vgetcpu_mode 218 .vsyscall_0 +0 .vsyscall_0 52 .vsyscall_1 +0 .vsyscall_1 91 .vsyscall_2 +0 .vsyscall_2 8 .vsyscall_3 +0 .vsyscall_3 54 .vsyscall_fn +0 .vsyscall_fn 80 .vsyscall_gtod_data +0 .vsyscall_gtod_data 39144 __bug_table +0 __bug_table 16320 __ex_table +0 __ex_table 44592 __ksymtab +0 __ksymtab 15200 __ksymtab_gpl +0 __ksymtab_gpl 48 __ksymtab_gpl_future +0 __ksymtab_gpl_future 87756 __ksymtab_strings +0 __ksymtab_strings 32 __ksymtab_unused_gpl +0 __ksymtab_unused_gpl 8280 __param +0 __param 7057383 Total +59 Total
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