perf_counter: new output ABI - part 1

Impact: Rework the perfcounter output ABI

use sys_read() only for instant data and provide mmap() output for all
async overflow data.

The first mmap() determines the size of the output buffer. The mmap()
size must be a PAGE_SIZE multiple of 1+pages, where pages must be a
power of 2 or 0. Further mmap()s of the same fd must have the same
size. Once all maps are gone, you can again mmap() with a new size.

In case of 0 extra pages there is no data output and the first page
only contains meta data.

When there are data pages, a poll() event will be generated for each
full page of data. Furthermore, the output is circular. This means
that although 1 page is a valid configuration, its useless, since
we'll start overwriting it the instant we report a full page.

Future work will focus on the output format (currently maintained)
where we'll likey want each entry denoted by a header which includes a
type and length.

Further future work will allow to splice() the fd, also containing the
async overflow data -- splice() would be mutually exclusive with
mmap() of the data.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Orig-LKML-Reference: <20090323172417.470536358@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
index e4349281b07d..d48596ab6557 100644
--- a/arch/powerpc/kernel/perf_counter.c
+++ b/arch/powerpc/kernel/perf_counter.c
@@ -417,8 +417,7 @@ void hw_perf_restore(u64 disable)
                 atomic64_set(&counter->hw.prev_count, val);
                 counter->hw.idx = hwc_index[i] + 1;
                 write_pmc(counter->hw.idx, val);
-                if (counter->user_page)
-                        perf_counter_update_userpage(counter);
+                perf_counter_update_userpage(counter);
         }
         mb();
         cpuhw->mmcr[0] |= MMCR0_PMXE | MMCR0_FCECE;
@@ -574,8 +573,7 @@ static void power_perf_disable(struct perf_counter *counter)
                         ppmu->disable_pmc(counter->hw.idx - 1, cpuhw->mmcr);
                         write_pmc(counter->hw.idx, 0);
                         counter->hw.idx = 0;
-                        if (counter->user_page)
-                                perf_counter_update_userpage(counter);
+                        perf_counter_update_userpage(counter);
                         break;
                 }
         }
@@ -702,8 +700,7 @@ static void record_and_restart(struct perf_counter *counter, long val,
         write_pmc(counter->hw.idx, val);
         atomic64_set(&counter->hw.prev_count, val);
         atomic64_set(&counter->hw.period_left, left);
-        if (counter->user_page)
-                perf_counter_update_userpage(counter);
+        perf_counter_update_userpage(counter);
 
         /*
          * Finally record data if requested.