On Thu, Mar 19, 2015 at 06:17:47PM +0100, Denys Vlasenko wrote: > With this change, on SYSCALL64 code path we are now populating > pt_regs->cs, pt_regs->ss and pt_regs->rcx unconditionally and > therefore don't need to do that in FIXUP_TOP_OF_STACK. > > We lose a number of large insns there: > > text data bss dec hex filename > 13298 0 0 13298 33f2 entry_64_before.o > 12978 0 0 12978 32b2 entry_64.o > > What's more important, we convert two "MOVQ $imm,off(%rsp)" to "PUSH $imm" > (the ones which fill pt_regs->cs,ss). > > Before this patch, placing them on fast path was slowing it down by two > cycles: > this form of MOV is very large, 12 bytes, and this probably reduces decode > bandwidth > to one insn per cycle when CPU sees them. > > Therefore they were living in FIXUP_TOP_OF_STACK instead (away from fast > path). > > "PUSH $imm" is a small 2-byte insn. Moving it to fast path does not slow it > down > in my measurements. > > Signed-off-by: Denys Vlasenko <[email protected]> > CC: Linus Torvalds <[email protected]> > CC: Steven Rostedt <[email protected]> > CC: Ingo Molnar <[email protected]> > CC: Borislav Petkov <[email protected]> > CC: "H. Peter Anvin" <[email protected]> > CC: Andy Lutomirski <[email protected]> > CC: Oleg Nesterov <[email protected]> > CC: Frederic Weisbecker <[email protected]> > CC: Alexei Starovoitov <[email protected]> > CC: Will Drewry <[email protected]> > CC: Kees Cook <[email protected]> > CC: [email protected] > CC: [email protected] > --- > > Changes since last version: reformulate old comment which was > mostly failing to explain why we don't have TRACE_IRQS_OFF/ONs > around a irq-off section in SYSCALL64 code path. > > arch/x86/kernel/entry_64.S | 54 > +++++++++++++++++++++++++++------------------- > 1 file changed, 32 insertions(+), 22 deletions(-)
Acked-by: Borislav Petkov <[email protected]> -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
