A performance counter of e500mc processor core generates an overflow interrupt when the counter value reaches to 0x80000000. In order to set up a sampling counter, the kernel sets the counter value to 0x80000000 - <samples> to cause an interrupt right after <samples> are incremented.
In the current code, the problem arises when the kernel stops and re-starts the sampling counter (fsl_emb_pmu_stop() and fsl_emb_pmu_start() are called repsectively). When fsl_emb_pmu_stop() is called, called when a user adjusts the sampling period, it currently re-writes the counter value to zero, which breaks working of the sampling counter. Similarily fsl_emb_pmu_start() re-write the counter value. This patch fixes the bug by not re-writing the counter unnecessarily. Also, it sets the counter freeze bit in fsl_emb_pmu_stop(), so that the counter does not increase until fsl_emb_pmu_start() is called again. Signed-off-by: Heechul Yun <[email protected]> --- arch/powerpc/perf/core-fsl-emb.c | 11 ++++++----- 1 files changed, 6 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/perf/core-fsl-emb.c b/arch/powerpc/perf/core-fsl-emb.c index 106c533..4cd4f12 100644 --- a/arch/powerpc/perf/core-fsl-emb.c +++ b/arch/powerpc/perf/core-fsl-emb.c @@ -365,7 +365,6 @@ static void fsl_emb_pmu_del(struct perf_event *event, int flags) static void fsl_emb_pmu_start(struct perf_event *event, int ef_flags) { unsigned long flags; - s64 left; if (event->hw.idx < 0 || !event->hw.sample_period) return; @@ -380,8 +379,9 @@ static void fsl_emb_pmu_start(struct perf_event *event, int ef_flags) perf_pmu_disable(event->pmu); event->hw.state = 0; - left = local64_read(&event->hw.period_left); - write_pmc(event->hw.idx, left); + + /* start the counter. */ + write_pmlca(event->hw.idx, event->hw.config_base); perf_event_update_userpage(event); perf_pmu_enable(event->pmu); @@ -403,7 +403,9 @@ static void fsl_emb_pmu_stop(struct perf_event *event, int ef_flags) fsl_emb_pmu_read(event); event->hw.state |= PERF_HES_STOPPED | PERF_HES_UPTODATE; - write_pmc(event->hw.idx, 0); + + /* freeze the counter. */ + write_pmlca(event->hw.idx, event->hw.config_base | PMLCA_FC); perf_event_update_userpage(event); perf_pmu_enable(event->pmu); @@ -575,7 +577,6 @@ static void record_and_restart(struct perf_event *event, unsigned long val, int record = 0; if (event->hw.state & PERF_HES_STOPPED) { - write_pmc(event->hw.idx, 0); return; } -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
