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 <dvlas...@redhat.com>
> CC: Linus Torvalds <torva...@linux-foundation.org>
> CC: Steven Rostedt <rost...@goodmis.org>
> CC: Ingo Molnar <mi...@kernel.org>
> CC: Borislav Petkov <b...@alien8.de>
> CC: "H. Peter Anvin" <h...@zytor.com>
> CC: Andy Lutomirski <l...@amacapital.net>
> CC: Oleg Nesterov <o...@redhat.com>
> CC: Frederic Weisbecker <fweis...@gmail.com>
> CC: Alexei Starovoitov <a...@plumgrid.com>
> CC: Will Drewry <w...@chromium.org>
> CC: Kees Cook <keesc...@chromium.org>
> CC: x...@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 <b...@suse.de>
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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