powerpc/pseries: Re-enable dispatch trace log userspace interface

Since the cpu accounting code uses the hypervisor dispatch trace log
now when CONFIG_VIRT_CPU_ACCOUNTING = y, the previous commit disabled
access to it via files in the /sys/kernel/debug/powerpc/dtl/ directory
in that case.  This restores those files.

To do this, we now have a hook that the cpu accounting code will call
as it processes each entry from the hypervisor dispatch trace log.
The code in dtl.c now uses that to fill up its ring buffer, rather
than having the hypervisor fill the ring buffer directly.

This also fixes dtl_file_read() to handle overflow conditions a bit
better and adds a spinlock to ensure that race conditions (multiple
processes opening or reading the file concurrently) are handled
correctly.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index fca20643c368..bcb738b9ff8c 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -183,6 +183,8 @@ DEFINE_PER_CPU(unsigned long, cputime_scaled_last_delta);
 
 cputime_t cputime_one_jiffy;
 
+void (*dtl_consumer)(struct dtl_entry *, u64);
+
 static void calc_cputime_factors(void)
 {
         struct div_result res;
@@ -218,7 +220,7 @@ static u64 read_spurr(u64 tb)
  */
 static u64 scan_dispatch_log(u64 stop_tb)
 {
-        unsigned long i = local_paca->dtl_ridx;
+        u64 i = local_paca->dtl_ridx;
         struct dtl_entry *dtl = local_paca->dtl_curr;
         struct dtl_entry *dtl_end = local_paca->dispatch_log_end;
         struct lppaca *vpa = local_paca->lppaca_ptr;
@@ -229,6 +231,8 @@ static u64 scan_dispatch_log(u64 stop_tb)
         if (i == vpa->dtl_idx)
                 return 0;
         while (i < vpa->dtl_idx) {
+                if (dtl_consumer)
+                        dtl_consumer(dtl, i);
                 dtb = dtl->timebase;
                 tb_delta = dtl->enqueue_to_dispatch_time +
                         dtl->ready_to_enqueue_time;