Subject: Re: [Cbe-oss-dev] [PATCH] Reworked Cell OProfile: SPU mutex lock fix

From: Maynard Johnson <[email-masked]>
Date: Thu, 24 Apr 2008 14:46:35 -0500

Carl Love wrote:
> This is a reworked patch to fix the SPU data storage.  Currently, the 
> SPU escape sequences and program counter data is being added directly 
> into the kernel buffer without holding the buffer_mutex lock.  This 
> patch changes how the data is stored.  A new function,
> oprofile_add_value, is added into the oprofile driver to allow adding
> generic data to the per cpu buffers.  This enables a series of calls
> to the oprofile_add_value to enter the needed SPU escape sequences 
> and SPU program data into the kernel buffer via the per cpu buffers
> without any additional processing. The oprofile_add_value function is
> generic so it could be used by other architecures as well provided
> the needed postprocessing was added to opreport.
>
> Finally, this patch backs out the changes previously added to the 
> oprofile generic code for handling the architecture specific 
> ops.sync_start and ops.sync_stop that allowed the architecture
> to skip the per CPU buffer creation.
>   
Looks good except for the few minor things noted below . . .

-Maynard
> Signed-off-by: Carl Love <[email-masked]>
>
> Index: Cell_kernel_4_15_2008/arch/powerpc/oprofile/cell/pr_util.h
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/arch/powerpc/oprofile/cell/pr_util.h
> +++ Cell_kernel_4_15_2008/arch/powerpc/oprofile/cell/pr_util.h
> @@ -20,11 +20,6 @@
>  #include <asm/cell-regs.h>
>  #include <asm/spu.h>
>
> -/* Defines used for sync_start */
> -#define SKIP_GENERIC_SYNC 0
> -#define SYNC_START_ERROR -1
> -#define DO_GENERIC_SYNC 1
> -
>  struct spu_overlay_info {	/* map of sections within an SPU overlay */
>  	unsigned int vma;	/* SPU virtual memory address from elf */
>  	unsigned int size;	/* size of section from elf */
> @@ -85,7 +80,7 @@ void stop_spu_profiling(void);
>  int spu_sync_start(void);
>
>  /* remove the hooks */
> -int spu_sync_stop(void);
> +void spu_sync_stop(void);
>
>  /* Record SPU program counter samples to the oprofile event buffer. */
>  void spu_sync_buffer(int spu_num, unsigned int *samples,
> Index: Cell_kernel_4_15_2008/arch/powerpc/oprofile/cell/spu_task_sync.c
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/arch/powerpc/oprofile/cell/spu_task_sync.c
> +++ Cell_kernel_4_15_2008/arch/powerpc/oprofile/cell/spu_task_sync.c
> @@ -31,11 +31,13 @@
>
>  #define RELEASE_ALL 9999
>
> -static DEFINE_SPINLOCK(buffer_lock);
> +static DEFINE_SPINLOCK(add_value_lock);
>  static DEFINE_SPINLOCK(cache_lock);
>  static int num_spu_nodes;
> +int per_cpu_buffers_exist=0;
>   
The per_cpu_buffers_exist variable is not used for anything useful -- a 
vestige of something done earlier, I think.
>  int spu_prof_num_nodes;
>  int last_guard_val[MAX_NUMNODES * 8];
> +static int spu_ctx_sw_seen[MAX_NUMNODES * 8];
>   
[snip]
>  int spu_sync_start(void)
>  {
>  	int k;
> -	int ret = SKIP_GENERIC_SYNC;
> +	int ret = 0;
>  	int register_ret;
> -	unsigned long flags = 0;
> +	int cpu;
>
>  	spu_prof_num_nodes = number_of_online_nodes();
>  	num_spu_nodes = spu_prof_num_nodes * 8;
>
> -	spin_lock_irqsave(&buffer_lock, flags);
> -	add_event_entry(ESCAPE_CODE);
> -	add_event_entry(SPU_PROFILING_CODE);
> -	add_event_entry(num_spu_nodes);
> -	spin_unlock_irqrestore(&buffer_lock, flags);
> +	/* At this point, the CPU buffers have been generated so
>   
Suggest you change "generated" to "allocated" for clarity.
> +	 * writes to the per CPU buffers can occur.  Need to
> +	 * set the flag that the buffers exist before registering for
> +	 * the SPU context switches or the routine to process the
> +	 * context switches will not write context switch information.
> +	 */
> +	per_cpu_buffers_exist = 1;
>   
delete
> +
> +	/* The SPU_PROFILING_CODE escape sequence must proceed
> +	 * the SPU context switch info.
> +	 */
> +	for_each_online_cpu(cpu) {
> +		oprofile_add_value(ESCAPE_CODE, cpu);
> +		oprofile_add_value(SPU_PROFILING_CODE, cpu);
> +		oprofile_add_value((unsigned long int)
> +					    num_spu_nodes, cpu);
> +	}
>
>  	/* Register for SPU events  */
>  	register_ret = spu_switch_event_register(&spu_active);
>  	if (register_ret) {
> -		ret = SYNC_START_ERROR;
> +		/* Stop the profile_spus() function from trying
> +		 * to store samples into the per CPU buffer.  The
> +		 * buffer will not be there.
> +		 */
> +		per_cpu_buffers_exist = 0;
>   
delete
> +		ret = -1;
>  		goto out;
>  	}
>
> -	for (k = 0; k < (MAX_NUMNODES * 8); k++)
> +	for (k = 0; k < (MAX_NUMNODES * 8); k++) {
>  		last_guard_val[k] = 0;
> +		spu_ctx_sw_seen[k] = 0;
> +	}
>  	pr_debug("spu_sync_start -- running.\n");
>  out:
>  	return ret;
> +
>  }
>
>  /* Record SPU program counter samples to the oprofile event buffer. */
> @@ -432,7 +460,7 @@ void spu_sync_buffer(int spu_num, unsign
>
>  	map = c_info->map;
>  	the_spu = c_info->the_spu;
> -	spin_lock(&buffer_lock);
> +	spin_lock(&add_value_lock);
>  	for (i = 0; i < num_samples; i++) {
>  		unsigned int sample = *(samples+i);
>  		int grd_val = 0;
> @@ -452,15 +480,22 @@ void spu_sync_buffer(int spu_num, unsign
>  			break;
>  		}
>
> -		add_event_entry(file_offset | spu_num_shifted);
>   
In our initial Cell SPU oprofile support submission to the kernel, we 
had added a prototype for add_event_entry to include/linux/oprofile.h .  
Now that this patch has replaced all uses of add_event_entry with the 
new oprofile_add_value function, we should remove the add_event_entry 
prototype from the header file -- especially since we were 
misusing/abusing it anyway (not grabbing the buffer_mutex before calling).
> +		/* We must ensure that the SPU context switch has been written
> +		 * out before samples for the SPU.  Otherwise, the SPU context
> +		 * information is not available and the postprocessing of the
> +		 * SPU PC will fail with no available anonymous map information.
> +		 */
> +		if (spu_ctx_sw_seen[spu_num])
> +			oprofile_add_value((file_offset | spu_num_shifted),
> +						    (spu_num >> 2));
>   
Carl, you and I had discussed earlier in a phone call how the above use 
of oprofile_add_value results in the CPU buffer space being used up 
twice as fast as normal (because of the implementation of 
oprofile_add_value writing a special ESCAPE code followed by the actual 
data).  Do we need to do something (either in userspace or kernel 
driver) to increase CPU buffer size?  Maybe on Cell BE, the default CPU 
buffer size should be doubled, but I don't think that could easily be 
done in the kernel driver.  Probably easier to add in the userspace tools.
>  	}
> -	spin_unlock(&buffer_lock);
> +	spin_unlock(&add_value_lock);
>  out:
>  	spin_unlock_irqrestore(&cache_lock, flags);
>  }
>
>
> -int spu_sync_stop(void)
> +void spu_sync_stop(void)
>  {
>  	unsigned long flags = 0;
>  	int ret = spu_switch_event_unregister(&spu_active);
>   
The variable 'ret' isn't needed anymore.  Maybe add a comment that we're 
intentionally ignoring return values from spu_switch_event_unregister 
and release_cached_info since we want/need generic sync_stop to run even 
if spu_sync_stop has a problem.
> @@ -475,8 +510,9 @@ int spu_sync_stop(void)
>  	ret = release_cached_info(RELEASE_ALL);
>  	spin_unlock_irqrestore(&cache_lock, flags);
>  out:
> +	per_cpu_buffers_exist = 0;
>   
delete
>  	pr_debug("spu_sync_stop -- done.\n");
> -	return ret;
> +	return;
>  }
>
>
> Index: Cell_kernel_4_15_2008/arch/powerpc/oprofile/op_model_cell.c
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/arch/powerpc/oprofile/op_model_cell.c
> +++ Cell_kernel_4_15_2008/arch/powerpc/oprofile/op_model_cell.c
> @@ -1191,15 +1191,15 @@ static int cell_sync_start(void)
>  	if (spu_cycle_reset)
>  		return spu_sync_start();
>  	else
> -		return DO_GENERIC_SYNC;
> +		return 0;
>  }
>
> -static int cell_sync_stop(void)
> +static void cell_sync_stop(void)
>  {
>  	if (spu_cycle_reset)
> -		return spu_sync_stop();
> -	else
> -		return 1;
> +		spu_sync_stop();
> +
> +	return;
>  }
>
>  struct op_powerpc_model op_model_cell = {
> Index: Cell_kernel_4_15_2008/drivers/oprofile/buffer_sync.c
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/drivers/oprofile/buffer_sync.c
> +++ Cell_kernel_4_15_2008/drivers/oprofile/buffer_sync.c
> @@ -521,6 +521,20 @@ void sync_buffer(int cpu)
>  			} else if (s->event == CPU_TRACE_BEGIN) {
>  				state = sb_bt_start;
>  				add_trace_begin();
> +			} else if (s->event == VALUE_HEADER_ID) {
> +				/* The next event contains a value
> +				 * to enter directly into the event buffer.
> +				 */
> +				increment_tail(cpu_buf);
> +				i++;  /* one less entry in buffer to process */
> +
> +				s = &cpu_buf->buffer[cpu_buf->tail_pos];
> +
> +				if (is_code(s->eip))
>   
This check seems sort of superfluous to me, but if you really want to 
keep it, make it an 'if (unlikely()) ' type of check.
> +					add_event_entry(s->event);
> +				else
> +					printk("KERN_ERR Oprofile per CPU" \
> +					       "buffer sequence error.\n");
>  			} else {
>  				struct mm_struct * oldmm = mm;
>
> Index: Cell_kernel_4_15_2008/drivers/oprofile/cpu_buffer.c
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/drivers/oprofile/cpu_buffer.c
> +++ Cell_kernel_4_15_2008/drivers/oprofile/cpu_buffer.c
> @@ -224,6 +224,35 @@ static void oprofile_end_trace(struct op
>  	cpu_buf->tracing = 0;
>  }
>
> +/*
> + * Add a value to the per CPU buffer.  The value is passed from the per CPU
> + * buffer to the kernel buffer with no additional processing.  The assumption
> + * is any processing of the value will be done in the postprocessor.  This
> + * function should only be used for special architecture specific data.
> + * Currently only used by the CELL processor.
> + *
> + * The first enty in the per cpu buffer consists of the escape code and
>   
"entry"
> + * the VALUE_HEADER_ID value.  The next entry consists of an escape code
> + * with the value to store.  The syn_buffer routine takes the value from
> + * the second entry and put it into the kernel buffer.
> + */
> +void oprofile_add_value(unsigned long value, int cpu) {
> +	struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[cpu];
> +
> +	/* Enter a sequence of two evnets.  The first event says the
>   
"events"
> +	 * next event contains a value that is to be put directly into the
> +	 * event buffer.
> +	 */
> +
> +	if (nr_available_slots(cpu_buf) < 3) {
> +		cpu_buf->sample_lost_overflow++;
> +		return;
> +	}
> +
> +	add_sample(cpu_buf, ESCAPE_CODE, VALUE_HEADER_ID);
> +	add_sample(cpu_buf, ESCAPE_CODE, value);
> +}
> +
>  void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
>  				unsigned long event, int is_kernel)
>  {
> Index: Cell_kernel_4_15_2008/drivers/oprofile/cpu_buffer.h
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/drivers/oprofile/cpu_buffer.h
> +++ Cell_kernel_4_15_2008/drivers/oprofile/cpu_buffer.h
> @@ -54,5 +54,6 @@ void cpu_buffer_reset(struct oprofile_cp
>  /* transient events for the CPU buffer -> event buffer */
>  #define CPU_IS_KERNEL 1
>  #define CPU_TRACE_BEGIN 2
> +#define VALUE_HEADER_ID 3
>
>  #endif /* OPROFILE_CPU_BUFFER_H */
> Index: Cell_kernel_4_15_2008/drivers/oprofile/oprof.c
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/drivers/oprofile/oprof.c
> +++ Cell_kernel_4_15_2008/drivers/oprofile/oprof.c
> @@ -53,24 +53,13 @@ int oprofile_setup(void)
>  	 * us missing task deaths and eventually oopsing
>  	 * when trying to process the event buffer.
>  	 */
> -	if (oprofile_ops.sync_start) {
> -		int sync_ret = oprofile_ops.sync_start();
> -		switch (sync_ret) {
> -		case 0:
> -			goto post_sync;
> -		case 1:
> -			goto do_generic;
> -		case -1:
> -			goto out3;
> -		default:
> -			goto out3;
> -		}
> -	}
> -do_generic:
> +	if (oprofile_ops.sync_start
> +	    && ((err = oprofile_ops.sync_start())))
> +		goto out2;
> +
>  	if ((err = sync_start()))
>  		goto out3;
>
> -post_sync:
>  	is_setup = 1;
>  	mutex_unlock(&start_mutex);
>  	return 0;
> @@ -133,20 +122,9 @@ out:
>  void oprofile_shutdown(void)
>  {
>  	mutex_lock(&start_mutex);
> -	if (oprofile_ops.sync_stop) {
> -		int sync_ret = oprofile_ops.sync_stop();
> -		switch (sync_ret) {
> -		case 0:
> -			goto post_sync;
> -		case 1:
> -			goto do_generic;
> -		default:
> -			goto post_sync;
> -		}
> -	}
> -do_generic:
> +	if (oprofile_ops.sync_stop)
> +		oprofile_ops.sync_stop();
>  	sync_stop();
> -post_sync:
>  	if (oprofile_ops.shutdown)
>  		oprofile_ops.shutdown();
>  	is_setup = 0;
> Index: Cell_kernel_4_15_2008/include/linux/oprofile.h
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/include/linux/oprofile.h
> +++ Cell_kernel_4_15_2008/include/linux/oprofile.h
>   
As mentioned above, the add_event_entry prototype should be removed from 
this header file.
> @@ -56,12 +56,10 @@ struct oprofile_operations {
>  	/* Stop delivering interrupts. */
>  	void (*stop)(void);
>  	/* Arch-specific buffer sync functions.
> -	 * Return value = 0:  Success
> -	 * Return value = -1: Failure
> -	 * Return value = 1:  Run generic sync function
> +	 * Sync start: Return 0 for Success,  -1 for Failure
>  	 */
>  	int (*sync_start)(void);
> -	int (*sync_stop)(void);
> +	void (*sync_stop)(void);
>
>  	/* Initiate a stack backtrace. Optional. */
>  	void (*backtrace)(struct pt_regs * const regs, unsigned int depth);
> @@ -106,6 +104,17 @@ void oprofile_add_sample(struct pt_regs 
>  void oprofile_add_ext_sample(unsigned long pc, struct pt_regs * const regs,
>  				unsigned long event, int is_kernel);
>
> +/*
> + * Add a value to the per CPU buffer.  The value is passed from the per CPU
> + * buffer to the kernel buffer with no additional processing.  The assumption
> + * is any processing of the value will be done in the postprocessor.  This
> + * function should only be used for special architecture specific data.
> + * Currently only used by the CELL processor.
> + *
> + * This function does not perform a backtrace.
> + */
> +void oprofile_add_value(unsigned long value, int cpu);
> +
>  /* Use this instead when the PC value is not from the regs. Doesn't
>   * backtrace. */
>  void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event);
> Index: Cell_kernel_4_15_2008/include/asm-powerpc/oprofile_impl.h
> ===================================================================
> --- Cell_kernel_4_15_2008.orig/include/asm-powerpc/oprofile_impl.h
> +++ Cell_kernel_4_15_2008/include/asm-powerpc/oprofile_impl.h
> @@ -48,7 +48,7 @@ struct op_powerpc_model {
>  	void (*stop) (void);
>  	void (*global_stop) (void);
>  	int (*sync_start)(void);
> -	int (*sync_stop)(void);
> +	void (*sync_stop)(void);
>  	void (*handle_interrupt) (struct pt_regs *,
>  				  struct op_counter_config *);
>  	int num_counters;
>
>
>
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