<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jan 28, 2015 at 9:56 PM, Sreejith M M <span dir="ltr"><<a href="mailto:sreejith.mm@gmail.com" target="_blank">sreejith.mm@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi,<br>
<br>
I was trying to understand the difference in scheduling between<br>
processes and threads(belong to same process).<br>
<br>
I was thinking that, when kernel has to switch to a task which belong<br>
to the same process, it does not have to clear / replace page global<br>
directories and other memory related information.<br>
<br>
But in switch_mm function some code is put under CONFIG_SMP function.<br>
What is its signigicance? Code is<br>
below(<a href="http://lxr.free-electrons.com/source/arch/x86/include/asm/mmu_context.h#L37" target="_blank">http://lxr.free-electrons.com/source/arch/x86/include/asm/mmu_context.h#L37</a>)<br>
.<br>
What I infer is that the code is doing flush tlb, reload page table<br>
directories etc in multiprocessor mode(obviously) but I believe this<br>
code may never be executed .<br>
<br>
Can anyone help to understand what this part of the function supposed to do?<br>
<br>
60 #ifdef CONFIG_SMP<br>
61 else {<br>
62 this_cpu_write(cpu_tlbstate.state, TLBSTATE_OK);<br>
63 BUG_ON(this_cpu_read(cpu_tlbstate.active_mm) != next);<br>
64<br>
65 if (!cpumask_test_cpu(cpu, mm_cpumask(next))) {<br>
66 /*<br>
67 * On established mms, the mm_cpumask is<br>
only changed<br>
68 * from irq context, from<br>
ptep_clear_flush() while in<br>
69 * lazy tlb mode, and here. Irqs are blocked during<br>
70 * schedule, protecting us from<br>
simultaneous changes.<br>
71 */<br>
72 cpumask_set_cpu(cpu, mm_cpumask(next));<br>
73 /*<br>
74 * We were in lazy tlb mode and leave_mm disabled<br>
75 * tlb flush IPI delivery. We must reload CR3<br>
76 * to make sure to use no freed page tables.<br>
77 */<br>
78 load_cr3(next->pgd);<br>
79 trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH,<br>
TLB_FLUSH_ALL);<br>
80 load_LDT_nolock(&next->context);<br>
81 }<br>
82 }<br>
83 #endif<br>
<span class="HOEnZb"><font color="#888888"><br>
<br>
--<br>
Regards,<br>
Sreejith<br>
</font></span></blockquote></div><br></div><div class="gmail_extra">Hi ,<br><br></div><div class="gmail_extra">can someone please give me any answers for this?<br clear="all"></div><div class="gmail_extra"><br>-- <br><div class="gmail_signature">Regards,<br>Sreejith</div>
</div></div>