x86/topology: Avoid wasting 128k for package id array

Analyzing large early boot allocations unveiled the logical package id
storage as a prominent memory waste. Since commit 1f12e32f4cd5
("x86/topology: Create logical package id") every 64-bit system allocates a
128k array to convert logical package ids.

This happens because the array is sized for MAX_LOCAL_APIC which is always
32k on 64bit systems, and it needs 4 bytes for each entry.

This is fairly wasteful, especially for the common case of having only one
socket, which uses exactly 4 byte out of 128K.

There is no user of the package id map which is performance critical, so
the lookup is not required to be O(1). Store the logical processor id in
cpu_data and use a loop based lookup.

To keep the mapping stable accross cpu hotplug operations, add a flag to
cpu_data which is set when the CPU is brought up the first time. When the
flag is set, then cpu_data is not reinitialized by copying boot_cpu_data on
subsequent bringups.

[ tglx: Rename the flag to 'initialized', use proper pointers instead of
  	repeated cpu_data(x) evaluation and massage changelog. ]

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: He Chen <he.chen@linux.intel.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Piotr Luc <piotr.luc@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arvind Yadav <arvind.yadav.cs@gmail.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Mathias Krause <minipli@googlemail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Link: https://lkml.kernel.org/r/20171114124257.22013-3-prarit@redhat.com

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 2db7cf720b04..cc16fa882e3e 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -132,6 +132,7 @@ struct cpuinfo_x86 {
 	/* Index into per_cpu list: */
 	u16			cpu_index;
 	u32			microcode;
+	unsigned		initialized : 1;
 } __randomize_layout;
 
 struct cpuid_regs {