Hi, I was trying to understand the difference in scheduling between processes and threads(belong to same process). I was thinking that, when kernel has to switch to a task which belong to the same process, it does not have to clear / replace page global directories and other memory related information. But in switch_mm function some code is put under CONFIG_SMP function. What is its signigicance? Code is below(http://lxr.free-electrons.com/source/arch/x86/include/asm/mmu_context.h#L37) . What I infer is that the code is doing flush tlb, reload page table directories etc in multiprocessor mode(obviously) but I believe this code may never be executed . Can anyone help to understand what this part of the function supposed to do? 60 #ifdef CONFIG_SMP 61 else { 62 this_cpu_write(cpu_tlbstate.state, TLBSTATE_OK); 63 BUG_ON(this_cpu_read(cpu_tlbstate.active_mm) != next); 64 65 if (!cpumask_test_cpu(cpu, mm_cpumask(next))) { 66 /* 67 * On established mms, the mm_cpumask is only changed 68 * from irq context, from ptep_clear_flush() while in 69 * lazy tlb mode, and here. Irqs are blocked during 70 * schedule, protecting us from simultaneous changes. 71 */ 72 cpumask_set_cpu(cpu, mm_cpumask(next)); 73 /* 74 * We were in lazy tlb mode and leave_mm disabled 75 * tlb flush IPI delivery. We must reload CR3 76 * to make sure to use no freed page tables. 77 */ 78 load_cr3(next->pgd); 79 trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); 80 load_LDT_nolock(&next->context); 81 } 82 } 83 #endif -- Regards, Sreejith