Re: [PATCH v2 01/13] coresight: trace-id: Add API to dynamically assign Trace ID values

[Suzuki K Poulose <suzuki.poulose@arm.com>]

Hi Mike,

Thanks for the patch, please find my comments inline.


On 04/07/2022 09:11, Mike Leach wrote:
> The existing mechanism to assign Trace ID values to sources is limited
> and does not scale for larger multicore / multi trace source systems.
> 
> The API introduces functions that reserve IDs based on availabilty
> represented by a coresight_trace_id_map structure. This records the
> used and free IDs in a bitmap.
> 
> CPU bound sources such as ETMs use the coresight_trace_id_get_cpu_id /
> coresight_trace_id_put_cpu_id pair of functions. The API will record
> the ID associated with the CPU. This ensures that the same ID will be
> re-used while perf events are active on the CPU. The put_cpu_id function
> will pend release of the ID until all perf cs_etm sessions are complete.
> 
> Non-cpu sources, such as the STM can use coresight_trace_id_get_system_id /
> coresight_trace_id_put_system_id.
> 
> Signed-off-by: Mike Leach <mike.leach@linaro.org>
> ---
>   drivers/hwtracing/coresight/Makefile          |   2 +-
>   .../hwtracing/coresight/coresight-trace-id.c  | 230 ++++++++++++++++++
>   .../hwtracing/coresight/coresight-trace-id.h  |  65 +++++
>   3 files changed, 296 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/hwtracing/coresight/coresight-trace-id.c
>   create mode 100644 drivers/hwtracing/coresight/coresight-trace-id.h
> 
> diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile
> index b6c4a48140ec..329a0c704b87 100644
> --- a/drivers/hwtracing/coresight/Makefile
> +++ b/drivers/hwtracing/coresight/Makefile
> @@ -6,7 +6,7 @@ obj-$(CONFIG_CORESIGHT) += coresight.o
>   coresight-y := coresight-core.o  coresight-etm-perf.o coresight-platform.o \
>   		coresight-sysfs.o coresight-syscfg.o coresight-config.o \
>   		coresight-cfg-preload.o coresight-cfg-afdo.o \
> -		coresight-syscfg-configfs.o
> +		coresight-syscfg-configfs.o coresight-trace-id.o
>   obj-$(CONFIG_CORESIGHT_LINK_AND_SINK_TMC) += coresight-tmc.o
>   coresight-tmc-y := coresight-tmc-core.o coresight-tmc-etf.o \
>   		      coresight-tmc-etr.o
> diff --git a/drivers/hwtracing/coresight/coresight-trace-id.c b/drivers/hwtracing/coresight/coresight-trace-id.c
> new file mode 100644
> index 000000000000..dac9c89ae00d
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/coresight-trace-id.c
> @@ -0,0 +1,230 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2022, Linaro Limited, All rights reserved.
> + * Author: Mike Leach <mike.leach@linaro.org>
> + */
> +#include <linux/kernel.h>
> +#include <linux/types.h>
> +#include <linux/spinlock.h>
> +
> +#include "coresight-trace-id.h"
> +
> +/* need to keep data on ids & association with cpus. */
> +struct cpu_id_info {
> +	int id;
> +	bool pend_rel;
> +};
> +
> +/* default trace ID map. Used for systems that do not require per sink mappings */
> +static struct coresight_trace_id_map id_map_default;
> +
> +/* maintain a record of the current mapping of cpu IDs */
> +static DEFINE_PER_CPU(struct cpu_id_info, cpu_ids);
> +
> +/* perf session active flag */
> +static int perf_cs_etm_session_active;
> +
> +/* lock to protect id_map and cpu data  */
> +static DEFINE_SPINLOCK(id_map_lock);
> +
> +/* ID 0 is reserved */
> +#define CORESIGHT_TRACE_ID_RES_0 0
> +
> +/* ID 0x70 onwards are reserved */
> +#define CORESIGHT_TRACE_ID_RES_RANGE_LO 0x70
> +#define CORESIGHT_TRACE_ID_RES_RANGE_HI 0x7F

Since this range is at the end of top, we could clip the
MAX_IDS to 0x70 and skip all these unnecessary checks and reservations.
Also, by modifying the find_bit and for_each_bit slightly we could
get away with this reservation scheme and the IS_VALID(id) checks.

> +#define IS_VALID_ID(id)	\
> +	((id > CORESIGHT_TRACE_ID_RES_0) && (id < CORESIGHT_TRACE_ID_RES_RANGE_LO))
> +
> +static void coresight_trace_id_set_inuse(int id, struct coresight_trace_id_map *id_map)
> +{
> +	if (IS_VALID_ID(id))
> +		set_bit(id, id_map->avail_ids);
> +}

Please see my comment around the definition of avail_ids.

> +
> +static void coresight_trace_id_clear_inuse(int id, struct coresight_trace_id_map *id_map)
> +{
> +	if (IS_VALID_ID(id))
> +		clear_bit(id, id_map->avail_ids);
> +}

This could be :

coresight_trace_id_free_id()

> +
> +static void coresight_trace_id_set_pend_rel(int id, struct coresight_trace_id_map *id_map)
> +{
> +	if (IS_VALID_ID(id))
> +		set_bit(id, id_map->pend_rel_ids);
> +}
> +
> +static void coresight_trace_id_clear_pend_rel(int id, struct coresight_trace_id_map *id_map)
> +{
> +	if (IS_VALID_ID(id))
> +		clear_bit(id, id_map->pend_rel_ids);
> +}
> +


> +static int coresight_trace_id_find_new_id(struct coresight_trace_id_map *id_map)

minor nit: Could we call this :

coresight_trace_id_alloc_new_id(id_map) and

> +{
> +	int id;
> +
> +	id = find_first_zero_bit(id_map->avail_ids, CORESIGHT_TRACE_IDS_MAX);

minor nit: You could also do, to explicitly skip 0.

     id = find_next_zero_bit(id_map->avail_ids, 1, CORESIGHT_TRACE_IDS_MAX);


> +	if (id >= CORESIGHT_TRACE_IDS_MAX)
> +		id = -EINVAL;

Could we also mark the id as in use here itself ? All callers of this 
function have to do that explicitly, anyways.

> +	return id;
> +}
> +
> +/* release all pending IDs for all current maps & clear CPU associations */
> +static void coresight_trace_id_release_all_pending(void)
> +{
> +	struct coresight_trace_id_map *id_map = &id_map_default;
> +	int cpu, bit;
> +
	int cpu, bit = 1;

> +	for_each_set_bit(bit, id_map->pend_rel_ids, CORESIGHT_TRACE_IDS_MAX) {

for_each_set_bit_from(bit, id_map...)

> +		clear_bit(bit, id_map->avail_ids);
> +		clear_bit(bit, id_map->pend_rel_ids);
> +	}
> +
> +	for_each_possible_cpu(cpu) {
> +		if (per_cpu(cpu_ids, cpu).pend_rel) {
> +			per_cpu(cpu_ids, cpu).pend_rel = false;
> +			per_cpu(cpu_ids, cpu).id = 0;
> +		}
> +	}
> +}
> +
> +static void coresight_trace_id_init_id_map(struct coresight_trace_id_map *id_map)
> +{
> +	int bit;
> +
> +	/* set all reserved bits as in-use */
> +	set_bit(CORESIGHT_TRACE_ID_RES_0, id_map->avail_ids);

> +	for (bit = CORESIGHT_TRACE_ID_RES_RANGE_LO;
> +	     bit <= CORESIGHT_TRACE_ID_RES_RANGE_HI; bit++)
> +		set_bit(bit, id_map->avail_ids);


> +}
> +
> +static int coresight_trace_id_map_get_cpu_id(int cpu, struct coresight_trace_id_map *id_map)
> +{
> +	unsigned long flags;
> +	int id;
> +
> +	spin_lock_irqsave(&id_map_lock, flags);
> +
> +	/* check for existing allocation for this CPU */
> +	id = per_cpu(cpu_ids, cpu).id;
> +	if (id)
> +		goto get_cpu_id_out;
> +
> +	/* find a new ID */
> +	id = coresight_trace_id_find_new_id(id_map);
> +	if (id < 0)
> +		goto get_cpu_id_out;
> +
> +	/* got a valid new ID - save details */
> +	per_cpu(cpu_ids, cpu).id = id;
> +	per_cpu(cpu_ids, cpu).pend_rel = false;
> +	coresight_trace_id_set_inuse(id, id_map);
> +	coresight_trace_id_clear_pend_rel(id, id_map);
> +
> +get_cpu_id_out:
> +	spin_unlock_irqrestore(&id_map_lock, flags);
> +	return id;
> +}
> +
> +static void coresight_trace_id_map_put_cpu_id(int cpu, struct coresight_trace_id_map *id_map)
> +{
> +	unsigned long flags;
> +	int id;
> +
> +	spin_lock_irqsave(&id_map_lock, flags);
> +	id = per_cpu(cpu_ids, cpu).id;
> +	if (!id)
> +		goto put_cpu_id_out;
> +
> +	if (perf_cs_etm_session_active) {
> +		/* set release at pending if perf still active */
> +		coresight_trace_id_set_pend_rel(id, id_map);
> +		per_cpu(cpu_ids, cpu).pend_rel = true;
> +	} else {
> +		/* otherwise clear id */
> +		coresight_trace_id_clear_inuse(id, id_map);
> +		per_cpu(cpu_ids, cpu).id = 0;
> +	}
> +
> + put_cpu_id_out:
> +	spin_unlock_irqrestore(&id_map_lock, flags);
> +}
> +
> +static int coresight_trace_id_map_get_system_id(struct coresight_trace_id_map *id_map)
> +{
> +	unsigned long flags;
> +	int id;
> +
> +	spin_lock_irqsave(&id_map_lock, flags);
> +	id = coresight_trace_id_find_new_id(id_map);
> +	if (id > 0)
> +		coresight_trace_id_set_inuse(id, id_map);

Please see my suggestion above on moving this to the place where we find 
the bit.

> +	spin_unlock_irqrestore(&id_map_lock, flags);
> +
> +	return id;
> +}
> +
> +static void coresight_trace_id_map_put_system_id(struct coresight_trace_id_map *id_map, int id)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&id_map_lock, flags);
> +	coresight_trace_id_clear_inuse(id, id_map);
> +	spin_unlock_irqrestore(&id_map_lock, flags);
> +}
> +
> +/* API functions */
> +int coresight_trace_id_get_cpu_id(int cpu)
> +{
> +	return coresight_trace_id_map_get_cpu_id(cpu, &id_map_default);
> +}
> +EXPORT_SYMBOL_GPL(coresight_trace_id_get_cpu_id);
> +
> +void coresight_trace_id_put_cpu_id(int cpu)
> +{
> +	coresight_trace_id_map_put_cpu_id(cpu, &id_map_default);
> +}
> +EXPORT_SYMBOL_GPL(coresight_trace_id_put_cpu_id);
> +
> +int coresight_trace_id_get_system_id(void)
> +{
> +	return coresight_trace_id_map_get_system_id(&id_map_default);
> +}
> +EXPORT_SYMBOL_GPL(coresight_trace_id_get_system_id);
> +
> +void coresight_trace_id_put_system_id(int id)
> +{
> +	coresight_trace_id_map_put_system_id(&id_map_default, id);
> +}
> +EXPORT_SYMBOL_GPL(coresight_trace_id_put_system_id);
> +
> +void coresight_trace_id_perf_start(void)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&id_map_lock, flags);
> +	perf_cs_etm_session_active++;
> +	spin_unlock_irqrestore(&id_map_lock, flags);
> +}
> +EXPORT_SYMBOL_GPL(coresight_trace_id_perf_start);
> +
> +void coresight_trace_id_perf_stop(void)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&id_map_lock, flags);
> +	perf_cs_etm_session_active--;
> +	if (!perf_cs_etm_session_active)
> +		coresight_trace_id_release_all_pending();
> +	spin_unlock_irqrestore(&id_map_lock, flags);
> +}
> +EXPORT_SYMBOL_GPL(coresight_trace_id_perf_stop);
> +
> +void coresight_trace_id_init_default_map(void)
> +{
> +	coresight_trace_id_init_id_map(&id_map_default);
> +}
> +EXPORT_SYMBOL_GPL(coresight_trace_id_init_default_map);

We may be able to get rid of this init. Otherwise we may convert this to
a module_initcall() in the worst case. No need to export this.

> diff --git a/drivers/hwtracing/coresight/coresight-trace-id.h b/drivers/hwtracing/coresight/coresight-trace-id.h
> new file mode 100644
> index 000000000000..63950087edf6
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/coresight-trace-id.h
> @@ -0,0 +1,65 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright(C) 2022 Linaro Limited. All rights reserved.
> + * Author: Mike Leach <mike.leach@linaro.org>
> + */
> +
> +#ifndef _CORESIGHT_TRACE_ID_H
> +#define _CORESIGHT_TRACE_ID_H
> +
> +/*
> + * Coresight trace ID allocation API
> + *
> + * With multi cpu systems, and more additional trace sources a scalable
> + * trace ID reservation system is required.
> + *
> + * The system will allocate Ids on a demand basis, and allow them to be
> + * released when done.
> + *
> + * In order to ensure that a consistent cpu / ID matching is maintained
> + * throughout a perf cs_etm event session - a session in progress flag will
> + * be maintained, and released IDs not cleared until the perf session is
> + * complete. This allows the same CPU to be re-allocated its prior ID.
> + *
> + *
> + * Trace ID maps will be created and initialised to prevent architecturally
> + * reserved IDs from being allocated.
> + *
> + * API permits multiple maps to be maintained - for large systems where
> + * different sets of cpus trace into different independent sinks.
> + */

Thanks for the detailed comment above.

> +
> +#include <linux/bitops.h>
> +#include <linux/types.h>
> +
> +
> +/* architecturally we have 128 IDs some of which are reserved */
> +#define CORESIGHT_TRACE_IDS_MAX 128

Could we restrict the CORESIGHT_TRACE_IDS_MAX to 0x70, clipping the 
upper range of reserved ids ? That way, we could skip bothering about
checking it everywhere.

> +
> +/**
> + * Trace ID map.
> + *
> + * @avail_ids:	Bitmap to register available (bit = 0) and in use (bit = 1) IDs.
> + *		Initialised so that the reserved IDs are permanently marked as in use.

To be honest this inverses the intution. Could we instead name this 
used_ids ?

i.e BIT(i) = 1 => implies trace id is in use.


> + * @pend_rel_ids: CPU IDs that have been released by the trace source but not yet marked
> + *                as available, to allow re-allocation to the same CPU during a perf session.
> + */
> +struct coresight_trace_id_map {
> +	DECLARE_BITMAP(avail_ids, CORESIGHT_TRACE_IDS_MAX);
> +	DECLARE_BITMAP(pend_rel_ids, CORESIGHT_TRACE_IDS_MAX);
> +};

Also, the definitions are split between the .c and .h. Could we keep all 
of them at one place, .h preferrably ? Or if this is not at all needed 
for the consumers of the API, we should keep all of this in the .c file.

I guess in the future, with the sink specific scheme, we may need to
expose the helpers which accept an id_map. So may be even move it here.


Thanks
Suzuki