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[PATCH] perf/x86/intel/uncore: fix broken read_counter() for SNB IMC PMU

Stephane Eranian posted 1 patch 3 years, 8 months ago 
arch/x86/events/intel/uncore_snb.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
[PATCH] perf/x86/intel/uncore: fix broken read_counter() for SNB IMC PMU
Posted by Stephane Eranian 3 years, 8 months ago 
Existing code was generating bogus counts for the SNB IMC bandwidth counters:

$ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
     1.000327813           1,024.03 MiB  uncore_imc/data_reads/
     1.000327813              20.73 MiB  uncore_imc/data_writes/
     2.000580153         261,120.00 MiB  uncore_imc/data_reads/
     2.000580153              23.28 MiB  uncore_imc/data_writes/

The problem was introduced by commit:
  07ce734dd8ad ("perf/x86/intel/uncore: Clean up client IMC")

Where the read_counter callback was replace to point to the generic
uncore_mmio_read_counter() function.

The SNB IMC counters are freerunnig 32-bit counters laid out contiguously in
MMIO. But uncore_mmio_read_counter() is using a readq() call to read from
MMIO therefore reading 64-bit from MMIO. Although this is okay for the
uncore_perf_event_update() function because it is shifting the value based
on the actual counter width to compute a delta, it is not okay for the
uncore_pmu_event_start() which is simply reading the counter  and therefore
priming the event->prev_count with a bogus value which is responsible for
causing bogus deltas in the perf stat command above.

The fix is to reintroduce the custom callback for read_counter for the SNB
IMC PMU and use readl() instead of readq(). With the change the output of
perf stat is back to normal:
$ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
     1.000120987             296.94 MiB  uncore_imc/data_reads/
     1.000120987             138.42 MiB  uncore_imc/data_writes/
     2.000403144             175.91 MiB  uncore_imc/data_reads/
     2.000403144              68.50 MiB  uncore_imc/data_writes/

Signed-off-by: Stephane Eranian <eranian@google.com>
---
 arch/x86/events/intel/uncore_snb.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/uncore_snb.c b/arch/x86/events/intel/uncore_snb.c
index ce440011cc4e..1ef4f7861e2e 100644
--- a/arch/x86/events/intel/uncore_snb.c
+++ b/arch/x86/events/intel/uncore_snb.c
@@ -841,6 +841,22 @@ int snb_pci2phy_map_init(int devid)
 	return 0;
 }
 
+static u64 snb_uncore_imc_read_counter(struct intel_uncore_box *box, struct perf_event *event)
+{
+	struct hw_perf_event *hwc = &event->hw;
+
+	/*
+	 * SNB IMC counters are 32-bit and are laid out back to back
+	 * in MMIO space. Therefore we must use a 32-bit accessor function
+	 * using readq() from uncore_mmio_read_counter() causes problems
+	 * because it is reading 64-bit at a time. This is okay for the
+	 * uncore_perf_event_update() function because it drops the upper
+	 * 32-bits but not okay for plain uncore_read_counter() as invoked
+	 * in uncore_pmu_event_start().
+	 */
+	return (u64)readl(box->io_addr + hwc->event_base);
+}
+
 static struct pmu snb_uncore_imc_pmu = {
 	.task_ctx_nr	= perf_invalid_context,
 	.event_init	= snb_uncore_imc_event_init,
@@ -860,7 +876,7 @@ static struct intel_uncore_ops snb_uncore_imc_ops = {
 	.disable_event	= snb_uncore_imc_disable_event,
 	.enable_event	= snb_uncore_imc_enable_event,
 	.hw_config	= snb_uncore_imc_hw_config,
-	.read_counter	= uncore_mmio_read_counter,
+	.read_counter	= snb_uncore_imc_read_counter,
 };
 
 static struct intel_uncore_type snb_uncore_imc = {
-- 
2.37.1.455.g008518b4e5-goog
Re: [PATCH] perf/x86/intel/uncore: fix broken read_counter() for SNB IMC PMU
Posted by Liang, Kan 3 years, 8 months ago 

On 2022-08-03 12:00 p.m., Stephane Eranian wrote:
> Existing code was generating bogus counts for the SNB IMC bandwidth counters:
> 
> $ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
>      1.000327813           1,024.03 MiB  uncore_imc/data_reads/
>      1.000327813              20.73 MiB  uncore_imc/data_writes/
>      2.000580153         261,120.00 MiB  uncore_imc/data_reads/
>      2.000580153              23.28 MiB  uncore_imc/data_writes/
> 
> The problem was introduced by commit:
>   07ce734dd8ad ("perf/x86/intel/uncore: Clean up client IMC")
> 
> Where the read_counter callback was replace to point to the generic
> uncore_mmio_read_counter() function.
> 
> The SNB IMC counters are freerunnig 32-bit counters laid out contiguously in
> MMIO. But uncore_mmio_read_counter() is using a readq() call to read from
> MMIO therefore reading 64-bit from MMIO. Although this is okay for the
> uncore_perf_event_update() function because it is shifting the value based
> on the actual counter width to compute a delta, it is not okay for the
> uncore_pmu_event_start() which is simply reading the counter  and therefore
> priming the event->prev_count with a bogus value which is responsible for
> causing bogus deltas in the perf stat command above.
> 
> The fix is to reintroduce the custom callback for read_counter for the SNB
> IMC PMU and use readl() instead of readq(). With the change the output of
> perf stat is back to normal:
> $ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
>      1.000120987             296.94 MiB  uncore_imc/data_reads/
>      1.000120987             138.42 MiB  uncore_imc/data_writes/
>      2.000403144             175.91 MiB  uncore_imc/data_reads/
>      2.000403144              68.50 MiB  uncore_imc/data_writes/
> 
> Signed-off-by: Stephane Eranian <eranian@google.com>

Reviewed-by: Kan Liang <kan.liang@linux.intel.com>

Thanks,
Kan

> ---
>  arch/x86/events/intel/uncore_snb.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/events/intel/uncore_snb.c b/arch/x86/events/intel/uncore_snb.c
> index ce440011cc4e..1ef4f7861e2e 100644
> --- a/arch/x86/events/intel/uncore_snb.c
> +++ b/arch/x86/events/intel/uncore_snb.c
> @@ -841,6 +841,22 @@ int snb_pci2phy_map_init(int devid)
>  	return 0;
>  }
>  
> +static u64 snb_uncore_imc_read_counter(struct intel_uncore_box *box, struct perf_event *event)
> +{
> +	struct hw_perf_event *hwc = &event->hw;
> +
> +	/*
> +	 * SNB IMC counters are 32-bit and are laid out back to back
> +	 * in MMIO space. Therefore we must use a 32-bit accessor function
> +	 * using readq() from uncore_mmio_read_counter() causes problems
> +	 * because it is reading 64-bit at a time. This is okay for the
> +	 * uncore_perf_event_update() function because it drops the upper
> +	 * 32-bits but not okay for plain uncore_read_counter() as invoked
> +	 * in uncore_pmu_event_start().
> +	 */
> +	return (u64)readl(box->io_addr + hwc->event_base);
> +}
> +
>  static struct pmu snb_uncore_imc_pmu = {
>  	.task_ctx_nr	= perf_invalid_context,
>  	.event_init	= snb_uncore_imc_event_init,
> @@ -860,7 +876,7 @@ static struct intel_uncore_ops snb_uncore_imc_ops = {
>  	.disable_event	= snb_uncore_imc_disable_event,
>  	.enable_event	= snb_uncore_imc_enable_event,
>  	.hw_config	= snb_uncore_imc_hw_config,
> -	.read_counter	= uncore_mmio_read_counter,
> +	.read_counter	= snb_uncore_imc_read_counter,
>  };
>  
>  static struct intel_uncore_type snb_uncore_imc = {
Re: [PATCH] perf/x86/intel/uncore: fix broken read_counter() for SNB IMC PMU
Posted by Stephane Eranian 3 years, 7 months ago 
On Thu, Aug 4, 2022 at 6:09 AM Liang, Kan <kan.liang@linux.intel.com> wrote:
>
>
>
> On 2022-08-03 12:00 p.m., Stephane Eranian wrote:
> > Existing code was generating bogus counts for the SNB IMC bandwidth counters:
> >
> > $ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
> >      1.000327813           1,024.03 MiB  uncore_imc/data_reads/
> >      1.000327813              20.73 MiB  uncore_imc/data_writes/
> >      2.000580153         261,120.00 MiB  uncore_imc/data_reads/
> >      2.000580153              23.28 MiB  uncore_imc/data_writes/
> >
> > The problem was introduced by commit:
> >   07ce734dd8ad ("perf/x86/intel/uncore: Clean up client IMC")
> >
> > Where the read_counter callback was replace to point to the generic
> > uncore_mmio_read_counter() function.
> >
> > The SNB IMC counters are freerunnig 32-bit counters laid out contiguously in
> > MMIO. But uncore_mmio_read_counter() is using a readq() call to read from
> > MMIO therefore reading 64-bit from MMIO. Although this is okay for the
> > uncore_perf_event_update() function because it is shifting the value based
> > on the actual counter width to compute a delta, it is not okay for the
> > uncore_pmu_event_start() which is simply reading the counter  and therefore
> > priming the event->prev_count with a bogus value which is responsible for
> > causing bogus deltas in the perf stat command above.
> >
> > The fix is to reintroduce the custom callback for read_counter for the SNB
> > IMC PMU and use readl() instead of readq(). With the change the output of
> > perf stat is back to normal:
> > $ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
> >      1.000120987             296.94 MiB  uncore_imc/data_reads/
> >      1.000120987             138.42 MiB  uncore_imc/data_writes/
> >      2.000403144             175.91 MiB  uncore_imc/data_reads/
> >      2.000403144              68.50 MiB  uncore_imc/data_writes/
> >
> > Signed-off-by: Stephane Eranian <eranian@google.com>
>
> Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
>
Any further comments?
Thanks.
Re: [PATCH] perf/x86/intel/uncore: fix broken read_counter() for SNB IMC PMU
Posted by Peter Zijlstra 3 years, 7 months ago 
On Mon, Aug 15, 2022 at 03:28:36PM -0700, Stephane Eranian wrote:
> On Thu, Aug 4, 2022 at 6:09 AM Liang, Kan <kan.liang@linux.intel.com> wrote:
> >
> >
> >
> > On 2022-08-03 12:00 p.m., Stephane Eranian wrote:
> > > Existing code was generating bogus counts for the SNB IMC bandwidth counters:
> > >
> > > $ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
> > >      1.000327813           1,024.03 MiB  uncore_imc/data_reads/
> > >      1.000327813              20.73 MiB  uncore_imc/data_writes/
> > >      2.000580153         261,120.00 MiB  uncore_imc/data_reads/
> > >      2.000580153              23.28 MiB  uncore_imc/data_writes/
> > >
> > > The problem was introduced by commit:
> > >   07ce734dd8ad ("perf/x86/intel/uncore: Clean up client IMC")
> > >
> > > Where the read_counter callback was replace to point to the generic
> > > uncore_mmio_read_counter() function.
> > >
> > > The SNB IMC counters are freerunnig 32-bit counters laid out contiguously in
> > > MMIO. But uncore_mmio_read_counter() is using a readq() call to read from
> > > MMIO therefore reading 64-bit from MMIO. Although this is okay for the
> > > uncore_perf_event_update() function because it is shifting the value based
> > > on the actual counter width to compute a delta, it is not okay for the
> > > uncore_pmu_event_start() which is simply reading the counter  and therefore
> > > priming the event->prev_count with a bogus value which is responsible for
> > > causing bogus deltas in the perf stat command above.
> > >
> > > The fix is to reintroduce the custom callback for read_counter for the SNB
> > > IMC PMU and use readl() instead of readq(). With the change the output of
> > > perf stat is back to normal:
> > > $ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
> > >      1.000120987             296.94 MiB  uncore_imc/data_reads/
> > >      1.000120987             138.42 MiB  uncore_imc/data_writes/
> > >      2.000403144             175.91 MiB  uncore_imc/data_reads/
> > >      2.000403144              68.50 MiB  uncore_imc/data_writes/
> > >
> > > Signed-off-by: Stephane Eranian <eranian@google.com>
> >
> > Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
> >
> Any further comments?

Got lost in the holiday pile-up, applied!
Re: [PATCH] perf/x86/intel/uncore: fix broken read_counter() for SNB IMC PMU
Posted by Stephane Eranian 3 years, 7 months ago 
On Thu, Aug 25, 2022 at 2:26 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Aug 15, 2022 at 03:28:36PM -0700, Stephane Eranian wrote:
> > On Thu, Aug 4, 2022 at 6:09 AM Liang, Kan <kan.liang@linux.intel.com> wrote:
> > >
> > >
> > >
> > > On 2022-08-03 12:00 p.m., Stephane Eranian wrote:
> > > > Existing code was generating bogus counts for the SNB IMC bandwidth counters:
> > > >
> > > > $ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
> > > >      1.000327813           1,024.03 MiB  uncore_imc/data_reads/
> > > >      1.000327813              20.73 MiB  uncore_imc/data_writes/
> > > >      2.000580153         261,120.00 MiB  uncore_imc/data_reads/
> > > >      2.000580153              23.28 MiB  uncore_imc/data_writes/
> > > >
> > > > The problem was introduced by commit:
> > > >   07ce734dd8ad ("perf/x86/intel/uncore: Clean up client IMC")
> > > >
> > > > Where the read_counter callback was replace to point to the generic
> > > > uncore_mmio_read_counter() function.
> > > >
> > > > The SNB IMC counters are freerunnig 32-bit counters laid out contiguously in
> > > > MMIO. But uncore_mmio_read_counter() is using a readq() call to read from
> > > > MMIO therefore reading 64-bit from MMIO. Although this is okay for the
> > > > uncore_perf_event_update() function because it is shifting the value based
> > > > on the actual counter width to compute a delta, it is not okay for the
> > > > uncore_pmu_event_start() which is simply reading the counter  and therefore
> > > > priming the event->prev_count with a bogus value which is responsible for
> > > > causing bogus deltas in the perf stat command above.
> > > >
> > > > The fix is to reintroduce the custom callback for read_counter for the SNB
> > > > IMC PMU and use readl() instead of readq(). With the change the output of
> > > > perf stat is back to normal:
> > > > $ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
> > > >      1.000120987             296.94 MiB  uncore_imc/data_reads/
> > > >      1.000120987             138.42 MiB  uncore_imc/data_writes/
> > > >      2.000403144             175.91 MiB  uncore_imc/data_reads/
> > > >      2.000403144              68.50 MiB  uncore_imc/data_writes/
> > > >
> > > > Signed-off-by: Stephane Eranian <eranian@google.com>
> > >
> > > Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
> > >
> > Any further comments?
>
> Got lost in the holiday pile-up, applied!

Thanks.
[tip: perf/urgent] perf/x86/intel/uncore: Fix broken read_counter() for SNB IMC PMU
Posted by tip-bot2 for Stephane Eranian 3 years, 7 months ago 
The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     11745ecfe8fea4b4a4c322967a7605d2ecbd5080
Gitweb:        https://git.kernel.org/tip/11745ecfe8fea4b4a4c322967a7605d2ecbd5080
Author:        Stephane Eranian <eranian@google.com>
AuthorDate:    Wed, 03 Aug 2022 09:00:31 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Sat, 27 Aug 2022 00:05:38 +02:00

perf/x86/intel/uncore: Fix broken read_counter() for SNB IMC PMU

Existing code was generating bogus counts for the SNB IMC bandwidth counters:

$ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
     1.000327813           1,024.03 MiB  uncore_imc/data_reads/
     1.000327813              20.73 MiB  uncore_imc/data_writes/
     2.000580153         261,120.00 MiB  uncore_imc/data_reads/
     2.000580153              23.28 MiB  uncore_imc/data_writes/

The problem was introduced by commit:
  07ce734dd8ad ("perf/x86/intel/uncore: Clean up client IMC")

Where the read_counter callback was replace to point to the generic
uncore_mmio_read_counter() function.

The SNB IMC counters are freerunnig 32-bit counters laid out contiguously in
MMIO. But uncore_mmio_read_counter() is using a readq() call to read from
MMIO therefore reading 64-bit from MMIO. Although this is okay for the
uncore_perf_event_update() function because it is shifting the value based
on the actual counter width to compute a delta, it is not okay for the
uncore_pmu_event_start() which is simply reading the counter  and therefore
priming the event->prev_count with a bogus value which is responsible for
causing bogus deltas in the perf stat command above.

The fix is to reintroduce the custom callback for read_counter for the SNB
IMC PMU and use readl() instead of readq(). With the change the output of
perf stat is back to normal:
$ perf stat -a -I 1000 -e uncore_imc/data_reads/,uncore_imc/data_writes/
     1.000120987             296.94 MiB  uncore_imc/data_reads/
     1.000120987             138.42 MiB  uncore_imc/data_writes/
     2.000403144             175.91 MiB  uncore_imc/data_reads/
     2.000403144              68.50 MiB  uncore_imc/data_writes/

Fixes: 07ce734dd8ad ("perf/x86/intel/uncore: Clean up client IMC")
Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/r/20220803160031.1379788-1-eranian@google.com
---
 arch/x86/events/intel/uncore_snb.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/uncore_snb.c b/arch/x86/events/intel/uncore_snb.c
index ce44001..1ef4f78 100644
--- a/arch/x86/events/intel/uncore_snb.c
+++ b/arch/x86/events/intel/uncore_snb.c
@@ -841,6 +841,22 @@ int snb_pci2phy_map_init(int devid)
 	return 0;
 }
 
+static u64 snb_uncore_imc_read_counter(struct intel_uncore_box *box, struct perf_event *event)
+{
+	struct hw_perf_event *hwc = &event->hw;
+
+	/*
+	 * SNB IMC counters are 32-bit and are laid out back to back
+	 * in MMIO space. Therefore we must use a 32-bit accessor function
+	 * using readq() from uncore_mmio_read_counter() causes problems
+	 * because it is reading 64-bit at a time. This is okay for the
+	 * uncore_perf_event_update() function because it drops the upper
+	 * 32-bits but not okay for plain uncore_read_counter() as invoked
+	 * in uncore_pmu_event_start().
+	 */
+	return (u64)readl(box->io_addr + hwc->event_base);
+}
+
 static struct pmu snb_uncore_imc_pmu = {
 	.task_ctx_nr	= perf_invalid_context,
 	.event_init	= snb_uncore_imc_event_init,
@@ -860,7 +876,7 @@ static struct intel_uncore_ops snb_uncore_imc_ops = {
 	.disable_event	= snb_uncore_imc_disable_event,
 	.enable_event	= snb_uncore_imc_enable_event,
 	.hw_config	= snb_uncore_imc_hw_config,
-	.read_counter	= uncore_mmio_read_counter,
+	.read_counter	= snb_uncore_imc_read_counter,
 };
 
 static struct intel_uncore_type snb_uncore_imc = {

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