Re: [PATCH] iommu/arm-smmu-v3: Add tracepoint for EVTQ events

[Robin Murphy <robin.murphy@arm.com>]

On 13/06/2026 2:00 pm, Chen Jun wrote:
> Events reported by the SMMU can severely impact accelerator
> performance. Currently, only events that the SMMU fails to handle are
> printed to the kernel log, leaving most events invisible to users.
> To analyze and optimize accelerator performance, complete visibility
> into all SMMU-reported events is required.

What events, exactly? AFAICS the only events we should expect to handle 
"invisibly", without being some unexpected error condition worth 
screaming about, would be stalls for SVA page faults, and if SVA isn't 
generically accounting page faults itself then I would imagine it 
probably should.

Thanks,
Robin.

> Add a tracepoint in the EVTQ interrupt handler to capture every
> event record reported by the SMMU. This allows users to collect all
> event information via ftrace/perf for further analysis, complementing
> the existing event decoder and error dump which only cover a subset
> of events.
> 
> Signed-off-by: Chen Jun <chenjun102@huawei.com>
> ---
>   drivers/iommu/arm/arm-smmu-v3/Makefile      |  2 +-
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c |  3 ++
>   drivers/iommu/arm/arm-smmu-v3/trace.c       |  9 ++++
>   drivers/iommu/arm/arm-smmu-v3/trace.h       | 53 +++++++++++++++++++++
>   4 files changed, 66 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/iommu/arm/arm-smmu-v3/trace.c
>   create mode 100644 drivers/iommu/arm/arm-smmu-v3/trace.h
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/Makefile b/drivers/iommu/arm/arm-smmu-v3/Makefile
> index 493a659cc66b..63a8d71bfc93 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/Makefile
> +++ b/drivers/iommu/arm/arm-smmu-v3/Makefile
> @@ -1,6 +1,6 @@
>   # SPDX-License-Identifier: GPL-2.0
>   obj-$(CONFIG_ARM_SMMU_V3) += arm_smmu_v3.o
> -arm_smmu_v3-y := arm-smmu-v3.o
> +arm_smmu_v3-y := arm-smmu-v3.o trace.o
>   arm_smmu_v3-$(CONFIG_ARM_SMMU_V3_IOMMUFD) += arm-smmu-v3-iommufd.o
>   arm_smmu_v3-$(CONFIG_ARM_SMMU_V3_SVA) += arm-smmu-v3-sva.o
>   arm_smmu_v3-$(CONFIG_TEGRA241_CMDQV) += tegra241-cmdqv.o
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index e8d7dbe495f0..85e6c25b73ed 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -34,6 +34,8 @@
>   #include "arm-smmu-v3.h"
>   #include "../../dma-iommu.h"
>   
> +#include "trace.h"
> +
>   static bool disable_msipolling;
>   module_param(disable_msipolling, bool, 0444);
>   MODULE_PARM_DESC(disable_msipolling,
> @@ -2271,6 +2273,7 @@ static irqreturn_t arm_smmu_evtq_thread(int irq, void *dev)
>   
>   	do {
>   		while (!queue_remove_raw(q, evt)) {
> +			trace_smmu_evtq_event(smmu, evt);
>   			arm_smmu_decode_event(smmu, evt, &event);
>   			if (arm_smmu_handle_event(smmu, evt, &event))
>   				arm_smmu_dump_event(smmu, evt, &event, &rs);
> diff --git a/drivers/iommu/arm/arm-smmu-v3/trace.c b/drivers/iommu/arm/arm-smmu-v3/trace.c
> new file mode 100644
> index 000000000000..77378698b1a3
> --- /dev/null
> +++ b/drivers/iommu/arm/arm-smmu-v3/trace.c
> @@ -0,0 +1,9 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * ARM SMMUv3 trace support
> + *
> + * Copyright (c) 2026 OpenCloudOS / openEuler
> + */
> +
> +#define CREATE_TRACE_POINTS
> +#include "trace.h"
> diff --git a/drivers/iommu/arm/arm-smmu-v3/trace.h b/drivers/iommu/arm/arm-smmu-v3/trace.h
> new file mode 100644
> index 000000000000..7cec8d41745e
> --- /dev/null
> +++ b/drivers/iommu/arm/arm-smmu-v3/trace.h
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * ARM SMMUv3 trace support
> + *
> + * Copyright (c) 2026 OpenCloudOS / openEuler
> + */
> +
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM arm_smmu_v3
> +
> +#if !defined(_TRACE_ARM_SMMU_V3_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_ARM_SMMU_V3_H
> +
> +#include <linux/tracepoint.h>
> +
> +#include "arm-smmu-v3.h"
> +
> +TRACE_EVENT(smmu_evtq_event,
> +
> +	TP_PROTO(struct arm_smmu_device *smmu, u64 *evt),
> +
> +	TP_ARGS(smmu, evt),
> +
> +	TP_STRUCT__entry(
> +		__string(iommu, dev_name(smmu->dev))
> +		__field(u64, evt0)
> +		__field(u64, evt1)
> +		__field(u64, evt2)
> +		__field(u64, evt3)
> +	),
> +
> +	TP_fast_assign(
> +		__assign_str(iommu);
> +		__entry->evt0 = evt[0];
> +		__entry->evt1 = evt[1];
> +		__entry->evt2 = evt[2];
> +		__entry->evt3 = evt[3];
> +	),
> +
> +	TP_printk("%s evt: 0x%016llx 0x%016llx 0x%016llx 0x%016llx",
> +		__get_str(iommu),
> +		__entry->evt0, __entry->evt1,
> +		__entry->evt2, __entry->evt3)
> +);
> +
> +#endif /* _TRACE_ARM_SMMU_V3_H */
> +
> +/* This part must be outside protection */
> +#undef TRACE_INCLUDE_PATH
> +#undef TRACE_INCLUDE_FILE
> +#define TRACE_INCLUDE_PATH ../../drivers/iommu/arm/arm-smmu-v3/
> +#define TRACE_INCLUDE_FILE trace
> +#include <trace/define_trace.h>