Subject: Re: [PATCH net-next 1/3] perf, events: add non-linear data support for raw records

From: Daniel Borkmann <[email-masked]>
Date: Wed, 13 Jul 2016 16:08:55 +0200

Hi Peter,

On 07/13/2016 03:42 PM, Peter Zijlstra wrote:
>
> Ok so the nonlinear thing was it doing _two_ copies, one the regular
> __output_copy() on raw->data and second the optional fragment thingy
> using __output_custom().
>
> Would something like this work instead?
>
> It does the nonlinear thing and the custom copy function thing but
> allows more than 2 fragments and allows each fragment to have a custom
> copy.
>
> It doesn't look obviously more expensive; it has the one ->copy branch
> extra, but then it doesn't recompute the sizes.

Yes, that would work as well on a quick glance with diff just a bit
bigger, but more generic this way. Do you want me to adapt this into
the first patch?

One question below:

> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 1fe22032f228..83e2a83e8db3 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -69,9 +69,18 @@ struct perf_callchain_entry_ctx {
>   	bool			    contexts_maxed;
>   };
>
> +typedef unsigned long (*perf_copy_f)(void *dst, const void *src, unsigned long len);
> +
> +struct perf_raw_frag {
> +	struct perf_raw_frag		*next;
> +	perf_copy_f			copy;
> +	void				*data;
> +	u32				size;
> +} __packed;
> +
>   struct perf_raw_record {
> +	struct perf_raw_frag		frag;
>   	u32				size;
> -	void				*data;
>   };
>
>   /*
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index fe8d49a56322..f7ad7d65317d 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5617,16 +5617,21 @@ void perf_output_sample(struct perf_output_handle *handle,
>   	}
>
>   	if (sample_type & PERF_SAMPLE_RAW) {
> -		if (data->raw) {
> -			u32 raw_size = data->raw->size;
> -			u32 real_size = round_up(raw_size + sizeof(u32),
> -						 sizeof(u64)) - sizeof(u32);
> -			u64 zero = 0;
> -
> -			perf_output_put(handle, real_size);
> -			__output_copy(handle, data->raw->data, raw_size);
> -			if (real_size - raw_size)
> -				__output_copy(handle, &zero, real_size - raw_size);
> +		struct perf_raw_record *raw = data->raw;
> +
> +		if (raw) {
> +			struct perf_raw_frag *frag = &raw->frag;
> +
> +			perf_output_put(handle, raw->size);
> +			do {
> +				if (frag->copy) {
> +					__output_custom(handle, frag->copy,
> +							frag->data, frag->size);
> +				} else {
> +					__output_copy(handle, frag->data, frag->size);
> +				}
> +				frag = frag->next;
> +			} while (frag);

We still need the zero padding here from above with the computed
raw->size, right?

>   		} else {
>   			struct {
>   				u32	size;
> @@ -5751,14 +5756,22 @@ void perf_prepare_sample(struct perf_event_header *header,

Thanks,
Daniel