Messages in this thread | | | Date | Tue, 28 Mar 2023 12:55:43 +0100 | From | Will Deacon <> | Subject | Re: [PATCH 2/3] perf/amlogic: Fix large number of counter issue |
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On Tue, Mar 28, 2023 at 10:29:04AM +0800, Jiucheng Xu wrote: > > My Amlogic email box has some issues. Use my personal email > <jiucheng.xu@163.com> to reply. > > On 2023/3/27 22:10, Will Deacon wrote: > > [ EXTERNAL EMAIL ] > > > > On Thu, Feb 09, 2023 at 07:54:02PM +0800, Jiucheng Xu wrote: > > > When use 1ms interval, very large number of counter happens > > > once in a while as below: > > > > > > 25.968654513 281474976710655.84 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/ > > > 26.118657346 281474976710655.88 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/ > > > 26.180137180 281474976710655.66 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/ > > > > > > Root cause is the race between irq handler > > > and pmu.read callback. Use spin lock to protect the sw&hw > > > counters. > > > > > > Signed-off-by: Jiucheng Xu <jiucheng.xu@amlogic.com> > > > --- > > > drivers/perf/amlogic/meson_ddr_pmu_core.c | 10 +++++++++- > > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/perf/amlogic/meson_ddr_pmu_core.c b/drivers/perf/amlogic/meson_ddr_pmu_core.c > > > index 0b24dee1ed3c..9b2e5d5c0626 100644 > > > --- a/drivers/perf/amlogic/meson_ddr_pmu_core.c > > > +++ b/drivers/perf/amlogic/meson_ddr_pmu_core.c > > > @@ -14,6 +14,7 @@ > > > #include <linux/perf_event.h> > > > #include <linux/platform_device.h> > > > #include <linux/printk.h> > > > +#include <linux/spinlock.h> > > > #include <linux/sysfs.h> > > > #include <linux/types.h> > > > @@ -23,6 +24,7 @@ struct ddr_pmu { > > > struct pmu pmu; > > > struct dmc_info info; > > > struct dmc_counter counters; /* save counters from hw */ > > > + spinlock_t lock; /* protect hw/sw counter */ > > > bool pmu_enabled; > > > struct device *dev; > > > char *name; > > > @@ -92,10 +94,12 @@ static void meson_ddr_perf_event_update(struct perf_event *event) > > > int idx; > > > int chann_nr = pmu->info.hw_info->chann_nr; > > > + spin_lock(&pmu->lock); > > Why doesn't this need the _irqsave() variant if we're racing with the irq > > handler? > > > > Will > I think meson_ddr_perf_event_update function is called with hard irq off. > So update function couldn't be interrupted by irq handler. Right?
I'm just confused about the race, then. The commit message says you have a race between an irq handler and a callback, which you fix with a spinlock that isn't irq safe. So either the race is real and the lock needs to be irqsafe, or the race is something else entirely, no?
Will
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