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Re: [Xen-devel] [PATCH 1/2] x86: during boot, anticipate identifying the boot cpu



On 08/25/2014 09:39 AM, Jan Beulich wrote:
On 22.08.14 at 19:15, <dario.faggioli@xxxxxxxxxx> wrote:
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1262,6 +1262,12 @@ void __init noreturn __start_xen(unsigned long mbi_p)
timer_init(); + /*
+     * Identify the boot CPU, in case the scheduler initialization
+     * needs to know about it (e.g., topology, etc.)
+     */
+    identify_cpu(&boot_cpu_data);
+
      init_idle_domain();
trap_init();
@@ -1272,8 +1278,6 @@ void __init noreturn __start_xen(unsigned long mbi_p)
arch_init_memory(); - identify_cpu(&boot_cpu_data);
-
      if ( cpu_has_fxsr )
          set_in_cr4(X86_CR4_OSFXSR);
      if ( cpu_has_xmm )
I'm not sure about this part: It currently makes quite a bit of sense
to have identify_cpu() immediately before explicit users of the
gathered data (all code following up to the alternative_instructions()
call). Perhaps if you move identify_cpu(), all the others should get
moved too?

Or possibly, move init_idle_domain() until after? I took a quick look through the functions called between init_idle_domain() and identify_cpu(), and didn't see any dependencies on the idle domain or scheduling functions. It's quite possible I missed something though.

Overall I think this approach looks good, and I agree with the comments already given.

 -George

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