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commit ad5d5292f16c6c1d7d3e257c4c7407594286b97e
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Author: Eric B Munson <emunson@mgebm.net>
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Date: Mon May 23 04:22:40 2011 +0000
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powerpc/oprofile: Handle events that raise an exception without overflowing
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Commit 0837e3242c73566fc1c0196b4ec61779c25ffc93 fixes a situation on POWER7
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where events can roll back if a specualtive event doesn't actually complete.
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This can raise a performance monitor exception. We need to catch this to ensure
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that we reset the PMC. In all cases the PMC will be less than 256 cycles from
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overflow.
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This patch lifts Anton's fix for the problem in perf and applies it to oprofile
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as well.
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Signed-off-by: Eric B Munson <emunson@mgebm.net>
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Cc: <stable@kernel.org> # as far back as it applies cleanly
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Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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diff --git a/arch/powerpc/oprofile/op_model_power4.c b/arch/powerpc/oprofile/op_model_power4.c
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index 8ee51a2..e6bec74 100644
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--- a/arch/powerpc/oprofile/op_model_power4.c
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+++ b/arch/powerpc/oprofile/op_model_power4.c
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@@ -261,6 +261,28 @@ static int get_kernel(unsigned long pc, unsigned long mmcra)
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return is_kernel;
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}
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+static bool pmc_overflow(unsigned long val)
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+{
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+ if ((int)val < 0)
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+ return true;
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+
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+ /*
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+ * Events on POWER7 can roll back if a speculative event doesn't
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+ * eventually complete. Unfortunately in some rare cases they will
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+ * raise a performance monitor exception. We need to catch this to
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+ * ensure we reset the PMC. In all cases the PMC will be 256 or less
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+ * cycles from overflow.
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+ *
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+ * We only do this if the first pass fails to find any overflowing
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+ * PMCs because a user might set a period of less than 256 and we
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+ * don't want to mistakenly reset them.
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+ */
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+ if (__is_processor(PV_POWER7) && ((0x80000000 - val) <= 256))
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+ return true;
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+
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+ return false;
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+}
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+
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static void power4_handle_interrupt(struct pt_regs *regs,
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struct op_counter_config *ctr)
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{
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@@ -281,7 +303,7 @@ static void power4_handle_interrupt(struct pt_regs *regs,
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for (i = 0; i < cur_cpu_spec->num_pmcs; ++i) {
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val = classic_ctr_read(i);
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- if (val < 0) {
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+ if (pmc_overflow(val)) {
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if (oprofile_running && ctr[i].enabled) {
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oprofile_add_ext_sample(pc, regs, i, is_kernel);
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classic_ctr_write(i, reset_value[i]);
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