Messages in this thread | | | Date | Tue, 7 Apr 2015 17:26:23 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86: simplify interrupt dispatch table |
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On Fri, Apr 03, 2015 at 09:49:13PM +0200, Denys Vlasenko wrote: > Interrupt entry points are handled with the following code: > Each 32-byte code block contains seven entry points > > ... > [push][jump 22] // 4 bytes > [push][jump 18] // 4 bytes > [push][jump 14] // 4 bytes > [push][jump 10] // 4 bytes > [push][jump 6] // 4 bytes > [push][jump 2] // 4 bytes > [push][jump common_interrupt][padding] // 8 bytes > > [push][jump] > [push][jump] > [push][jump] > [push][jump] > [push][jump] > [push][jump] > [push][jump common_interrupt][padding] > > [padding_2] > common_interrupt: > > And there is a table which holds pointers to every entry point, > IOW: to every push. > > In cold cache, two jumps are still costlier than one, even though we get > the benefit of them residing in the same cacheline. > > This change replaces short jumps with near ones to common_interrupt, and pads > every push+jump pair to 8 bytes. This way, each interrupt takes only one jump. > > This change replaces ".p2align CONFIG_X86_L1_CACHE_SHIFT" before dispatch table > with ".align 8" - we do not need anything stronger than that. > > The table of entry addresses (the interrupt[] array) is no longer > necessary, the address of entries can be easily calculated as > (irq_entries_start + i*8). > > text data bss dec hex filename > 12546 0 0 12546 3102 entry_64.o.before > 11626 0 0 11626 2d6a entry_64.o > > The size decrease is because 1656 bytes of .init.rodata are gone. > That's initdata, though. The resident size does go up a bit. > > Run-tested (32 and 64 bits). > > Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com> > CC: Linus Torvalds <torvalds@linux-foundation.org> > CC: Steven Rostedt <rostedt@goodmis.org> > CC: Ingo Molnar <mingo@kernel.org> > CC: Borislav Petkov <bp@alien8.de> > CC: "H. Peter Anvin" <hpa@zytor.com> > CC: Andy Lutomirski <luto@amacapital.net> > CC: Oleg Nesterov <oleg@redhat.com> > CC: Frederic Weisbecker <fweisbec@gmail.com> > CC: Alexei Starovoitov <ast@plumgrid.com> > CC: Will Drewry <wad@chromium.org> > CC: Kees Cook <keescook@chromium.org> > CC: x86@kernel.org > CC: linux-kernel@vger.kernel.org > --- > arch/x86/include/asm/hw_irq.h | 5 ++--- > arch/x86/kernel/entry_32.S | 41 ++++++++++------------------------------- > arch/x86/kernel/entry_64.S | 41 ++++++++++------------------------------- > arch/x86/kernel/irqinit.c | 3 ++- > arch/x86/lguest/boot.c | 3 ++- > 5 files changed, 26 insertions(+), 67 deletions(-)
Acked-and-tested-by: Borislav Petkov <bp@suse.de>
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply. --
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