[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>

2 files changed, 39 insertions, 5 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
diff --git a/arch/s390/kernel/vdso64/clock_gettime.S b/arch/s390/kernel/vdso64/clock_gettime.S
index 738a410b7eb2..79dbfee831ec 100644
--- a/arch/s390/kernel/vdso64/clock_gettime.S
+++ b/arch/s390/kernel/vdso64/clock_gettime.S
@@ -22,8 +22,10 @@ __kernel_clock_gettime:
         larl    %r5,_vdso_data
         cghi    %r2,CLOCK_REALTIME
         je      4f
+        cghi    %r2,-2          /* CLOCK_THREAD_CPUTIME_ID for this thread */
+        je      9f
         cghi    %r2,CLOCK_MONOTONIC
-        jne     9f
+        jne     12f
 
         /* CLOCK_MONOTONIC */
         ltgr    %r3,%r3
@@ -42,7 +44,7 @@ __kernel_clock_gettime:
         alg     %r0,__VDSO_WTOM_SEC(%r5)
         clg     %r4,__VDSO_UPD_COUNT(%r5)       /* check update counter */
         jne     0b
-        larl    %r5,10f
+        larl    %r5,13f
 1:      clg     %r1,0(%r5)
         jl      2f
         slg     %r1,0(%r5)
@@ -68,7 +70,7 @@ __kernel_clock_gettime:
         lg      %r0,__VDSO_XTIME_SEC(%r5)
         clg     %r4,__VDSO_UPD_COUNT(%r5)       /* check update counter */
         jne     5b
-        larl    %r5,10f
+        larl    %r5,13f
 6:      clg     %r1,0(%r5)
         jl      7f
         slg     %r1,0(%r5)
@@ -79,11 +81,38 @@ __kernel_clock_gettime:
 8:      lghi    %r2,0
         br      %r14
 
+        /* CLOCK_THREAD_CPUTIME_ID for this thread */
+9:      icm     %r0,15,__VDSO_ECTG_OK(%r5)
+        jz      12f
+        ear     %r2,%a4
+        llilh   %r4,0x0100
+        sar     %a4,%r4
+        lghi    %r4,0
+        sacf    512                             /* Magic ectg instruction */
+        .insn   ssf,0xc80100000000,__VDSO_ECTG_BASE(4),__VDSO_ECTG_USER(4),4
+        sacf    0
+        sar     %a4,%r2
+        algr    %r1,%r0                         /* r1 = cputime as TOD value */
+        mghi    %r1,1000                        /* convert to nanoseconds */
+        srlg    %r1,%r1,12                      /* r1 = cputime in nanosec */
+        lgr     %r4,%r1
+        larl    %r5,13f
+        srlg    %r1,%r1,9                       /* divide by 1000000000 */
+        mlg     %r0,8(%r5)
+        srlg    %r0,%r0,11                      /* r0 = tv_sec */
+        stg     %r0,0(%r3)
+        msg     %r0,0(%r5)                      /* calculate tv_nsec */
+        slgr    %r4,%r0                         /* r4 = tv_nsec */
+        stg     %r4,8(%r3)
+        lghi    %r2,0
+        br      %r14
+
         /* Fallback to system call */
-9:      lghi    %r1,__NR_clock_gettime
+12:     lghi    %r1,__NR_clock_gettime
         svc     0
         br      %r14
 
-10:     .quad   1000000000
+13:     .quad   1000000000
+14:     .quad   19342813113834067
         .cfi_endproc
         .size   __kernel_clock_gettime,.-__kernel_clock_gettime