ARM: vfp: Record VFP bounces as perf emulation faults

VFP 'bouncing' occurs when the VFP unit cannot complete the execution of
a VFP instruction, either because it is not implemented at all, or
because the values of the arguments are out of range for the hardware
implementation, and the software needs to step in to complete the
operation.

To give some insight in how much certain programs rely on this bouncing,
record the emulation of a VFP instruction in perf's emulation-faults
counter.

This can be used like so

  perf stat -e emulation-faults ./testfloat -all2

and the output will be something like

 Performance counter stats for './testfloat -all2':

           259,277      emulation-faults:u

       6.846432176 seconds time elapsed

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 349dcb9..08d5dfc 100644 (file)
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -18,6 +18,7 @@
 #include <linux/uaccess.h>
 #include <linux/user.h>
 #include <linux/export.h>
+#include <linux/perf_event.h>
 
 #include <asm/cp15.h>
 #include <asm/cputype.h>
@@ -313,6 +314,7 @@ static u32 vfp_emulate_instruction(u32 inst, u32 fpscr, struct pt_regs *regs)
                 * emulate it.
                 */
        }
+       perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
        return exceptions & ~VFP_NAN_FLAG;
 }