[PATCH] fast vdso implementation for CLOCK_THREAD_CPUTIME_ID

The extract cpu time instruction (ectg) instruction allows the user
process to get the current thread cputime without calling into the
kernel. The code that uses the instruction needs to switch to the
access registers mode to get access to the per-cpu info page that
contains the two base values that are needed to calculate the current
cputime from the CPU timer with the ectg instruction.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/arch/s390/kernel/vdso64/clock_getres.S b/arch/s390/kernel/vdso64/clock_getres.S
index 488e31a3c0e7..9ce8caafdb4e 100644
--- a/arch/s390/kernel/vdso64/clock_getres.S
+++ b/arch/s390/kernel/vdso64/clock_getres.S
@@ -22,7 +22,12 @@ __kernel_clock_getres:
         cghi    %r2,CLOCK_REALTIME
         je      0f
         cghi    %r2,CLOCK_MONOTONIC
+        je      0f
+        cghi    %r2,-2          /* CLOCK_THREAD_CPUTIME_ID for this thread */
         jne     2f
+        larl    %r5,_vdso_data
+        icm     %r0,15,__LC_ECTG_OK(%r5)
+        jz      2f
 0:      ltgr    %r3,%r3
         jz      1f                              /* res == NULL */
         larl    %r1,3f