>hm, DEFINE_PER_CPU_SHARED_CACHELINE_ALIGNED is a bit of a mouthful. >I wonder if we can improve things here so that we use the runtime-detected >cacheline size rather than the compile-time size. I guess not, given that >the offsets into the percpu area are calculated at build-time.
>Did you work out how much space this change will actually save? It >should be available by suitable crunching on the nm and objdump output. Depending on how data fields are arranged by linker, the patches could save or waste per_cpu size. Below is data I got. Case 1: On linux-2.6.21-rc7-mm2 with defconfig build. Case 2: On linux-2.6.21-rc7-mm2 plus the patches in this thread with defconfig build. Case 3: On linux-2.6.21-rc7-mm2 with defconfig with VSMP=y build. Case 4: On linux-2.6.21-rc7-mm2 plus the patches in this thread with defconfig with VSMP=y build. Please note that on x86/x86-64, per_cpu_init_tss is placed in the first place in per_cpu section in Case 1 and 3. And thus there is no padding waste for per_cpu_init_tss in Case 1 and 3. On X86: Case 1: Size of per_cpu section is: 0x7768 Case 2: Size of per_cpu section is: 0x790c The patches waste 0x1a4 bytes. per_cpu__init_tss, per_cpu__irq_stat, and per_cpu__runqueues are moved to shared_cacheline_aligned section. On X86-64: Case 1: Size of per_cpu section is: 0x72d0 Case 2: Size of per_cpu section is: 0x6540 The patches save 0xd90 bytes. Case 3: Size of per_cpu section is: 0x72d0 Case 4: Size of per_cpu section is: 0x8340 The patches waste 0x1070 bytes. Shall we not use shared_cacheline_aligned section for VSMP case? The waste of cache eventually may offset the potential gain of alignment. Probably need to set up a cache line size threshold: if L1 cache line size is bigger than a number CACHELINE_ALIGN_SHRESHOLD, don't do cacheline alignment. per_cpu__init_tss and per_cpu__runqueues are moved to shared_cacheline_aligned section. On ia64: Case 1: Size of per_cpu section is: 0x8370 Case 2: Size of per_cpu section is: 0x7fc0 The patches save 0x3b0 bytes. per_cpu_ipi_operation and per_cpu_runqueues are moved to shared_cacheline_aligned section - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
