Zachary Amsden e9f86e351f [PATCH] x86: remove redundant TSS clearing ... When reviewing GDT updates, I found the code: set_tss_desc(cpu,t); /* This just modifies memory; ... */ per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS].b &= 0xfffffdff; This second line is unnecessary, since set_tss_desc() has already cleared the busy bit. Commented disassembly, line 1: c028b8bd: 8b 0c 86 mov (%esi,%eax,4),%ecx c028b8c0: 01 cb add %ecx,%ebx c028b8c2: 8d 0c 39 lea (%ecx,%edi,1),%ecx => %ecx = per_cpu(cpu_gdt_table, cpu) c028b8c5: 8d 91 80 00 00 00 lea 0x80(%ecx),%edx => %edx = &per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS] c028b8cb: 66 c7 42 00 73 20 movw $0x2073,0x0(%edx) c028b8d1: 66 89 5a 02 mov %bx,0x2(%edx) c028b8d5: c1 cb 10 ror $0x10,%ebx c028b8d8: 88 5a 04 mov %bl,0x4(%edx) c028b8db: c6 42 05 89 movb $0x89,0x5(%edx) => ((char *)%edx)[5] = 0x89 (equivalent) ((char *)per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS])[5] = 0x89 c028b8df: c6 42 06 00 movb $0x0,0x6(%edx) c028b8e3: 88 7a 07 mov %bh,0x7(%edx) c028b8e6: c1 cb 10 ror $0x10,%ebx => other bits Commented disassembly, line 2: c028b8e9: 8b 14 86 mov (%esi,%eax,4),%edx c028b8ec: 8d 04 3a lea (%edx,%edi,1),%eax => %eax = per_cpu(cpu_gdt_table, cpu) c028b8ef: 81 a0 84 00 00 00 ff andl $0xfffffdff,0x84(%eax) => per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS].b &= 0xfffffdff; (equivalent) ((char *)per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS])[5] &= 0xfd Note that (0x89 & ~0xfd) == 0; i.e, set_tss_desc(cpu,t) has already stored the type field in the GDT with the busy bit clear. Eliminating redundant and obscure code is always a good thing; in fact, I pointed out this same optimization many moons ago in arch/i386/setup.c, back when it used to be called that. Signed-off-by: Zachary Amsden <zach@vmware.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>		2005-09-05 00:06:13 -07:00
..
cpu.c	[PATCH] x86: remove redundant TSS clearing	2005-09-05 00:06:13 -07:00
Makefile
swsusp.S