linux-kernel - Re: [PATCH] usb: gadget: functions: add ftrace export over USB

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Message-ID: <16a6940d-d071-cd2d-5911-dad427a13cb0@redhat.com>
Date:   Fri, 14 Jul 2017 11:01:35 +0530
From:   Pratyush Anand <panand@...hat.com>
To:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Linux USB <linux-usb@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Chunyan Zhang <zhang.chunyan@...aro.org>
Subject: Re: [PATCH] usb: gadget: functions: add ftrace export over USB

Hi Felipe,

On Friday 09 June 2017 11:43 AM, Felipe Balbi wrote:
> +static void notrace ftrace_write(struct trace_export *ftrace, const void *buf,
> +				 unsigned int len)
> +{
> +	struct usb_ftrace		*trace = ftrace_to_trace(ftrace);
> +	struct usb_request		*req = next_request(&trace->list);
> +
> +	if (!req)
> +		return;
> +
> +	if (!trace->in->enabled)
> +		return;
> +
> +	req->buf = kmemdup(buf, len, GFP_ATOMIC);

Probably we can avoid the copy of trace data.

We can make write() call of "struct trace_export" as posted. Can have a 
write_complete() callback function implemented in  struct trace_export,which 
can be called from your ftrace_complete().

We need to execute __buffer_unlock_commit() only in write_complete() in case 
of ftrace_export is enabled.


> +	req->length = len;
> +	req->context = trace;
> +	req->complete = ftrace_complete;
> +	list_move_tail(&req->list, &trace->pending);
> +
> +	schedule_work(&trace->queue_work);
> +}
> +

--
Pratyush