linux-kernel - Re: [PATCH v2 3/5] hwtracing: hisi_ptt: Optimize the trace data committing

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Message-ID: <03da788f-584b-1be5-2cc3-70a9e57c11ba@arm.com>
Date:   Fri, 15 Sep 2023 15:44:43 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Yicong Yang <yangyicong@...wei.com>, mathieu.poirier@...aro.org,
        jonathan.cameron@...wei.com, linux-kernel@...r.kernel.org
Cc:     alexander.shishkin@...ux.intel.com, helgaas@...nel.org,
        linux-pci@...r.kernel.org, prime.zeng@...ilicon.com,
        linuxarm@...wei.com, yangyicong@...ilicon.com, hejunhao3@...wei.com
Subject: Re: [PATCH v2 3/5] hwtracing: hisi_ptt: Optimize the trace data
 committing

On 14/09/2023 12:22, Yicong Yang wrote:
> From: Yicong Yang <yangyicong@...ilicon.com>
> 
> Currently during the PTT trace, we'll only commit the data
> to the perf core when its full, which means after 4 interrupts
> and totally 16MiB data while the AUX buffer is 16MiB length.
> Then the userspace gets notified and handle the data. The driver
> cannot apply a new AUX buffer immediately until the committed data
> are handled and there's enough room in the buffer again.
> 
> This patch tries to optimize this by commit the data in every
> interrupts in a 4MiB granularity. Then the userspace can have
> enough time to consume the data and there's always enough room
> in the AUX buffer.

Instead of always committing at 4M, could we not use the existing
markers used by the handle->wakeup to decide if we should commit it ?


Suzuki

> 
> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
> Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
>   drivers/hwtracing/ptt/hisi_ptt.c | 15 +++++++--------
>   1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/hwtracing/ptt/hisi_ptt.c b/drivers/hwtracing/ptt/hisi_ptt.c
> index 3041238a6e54..4f355df8da23 100644
> --- a/drivers/hwtracing/ptt/hisi_ptt.c
> +++ b/drivers/hwtracing/ptt/hisi_ptt.c
> @@ -274,15 +274,14 @@ static int hisi_ptt_update_aux(struct hisi_ptt *hisi_ptt, int index, bool stop)
>   	buf->pos += size;
>   
>   	/*
> -	 * Just commit the traced data if we're going to stop. Otherwise if the
> -	 * resident AUX buffer cannot contain the data of next trace buffer,
> -	 * apply a new one.
> +	 * Always commit the data to the AUX buffer in time to make sure
> +	 * userspace got enough time to consume the data.
> +	 *
> +	 * If we're not going to stop, apply a new one and check whether
> +	 * there's enough room for the next trace.
>   	 */
> -	if (stop) {
> -		perf_aux_output_end(handle, buf->pos);
> -	} else if (buf->length - buf->pos < HISI_PTT_TRACE_BUF_SIZE) {
> -		perf_aux_output_end(handle, buf->pos);
> -
> +	perf_aux_output_end(handle, size);
> +	if (!stop) {
>   		buf = perf_aux_output_begin(handle, event);
>   		if (!buf)
>   			return -EINVAL;