Date:	Wed, 25 Nov 2015 16:54:09 +0000
From:	Felipe Ferreri Tonello <eu@...ipetonello.com>
To:	Robert Baldyga <r.baldyga@...sung.com>, linux-usb@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Clemens Ladisch <clemens@...isch.de>
Subject: Re: [PATCH v5 7/7] usb: gadget: f_midi: pre-allocate IN requests

Hi Robert,

On 13/11/15 12:38, Robert Baldyga wrote:
> Hi Felipe,
> 
> On 11/10/2015 06:52 PM, Felipe F. Tonello wrote:
>> This patch introduces pre-allocation of IN endpoint USB requests. This
>> improves on latency (requires no usb request allocation on transmit) and avoid
>> several potential probles on allocating too many usb requests (which involves
>> DMA pool allocation problems).
>>
>> This implementation also handles better multiple MIDI Gadget ports, always
>> processing the last processed MIDI substream if the last USB request wasn't
>> enought to handle the whole stream.
>>
>> Signed-off-by: Felipe F. Tonello <eu@...ipetonello.com>
>> ---
>>  drivers/usb/gadget/function/f_midi.c | 174 +++++++++++++++++++++++++++--------
>>  drivers/usb/gadget/legacy/gmidi.c    |   2 +-
>>  2 files changed, 137 insertions(+), 39 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
>> index 615d632..6ac39f6 100644
>> --- a/drivers/usb/gadget/function/f_midi.c
>> +++ b/drivers/usb/gadget/function/f_midi.c
>> @@ -23,6 +23,7 @@
>>  #include <linux/module.h>
>>  #include <linux/slab.h>
>>  #include <linux/device.h>
>> +#include <linux/kfifo.h>
>>  
>>  #include <sound/core.h>
>>  #include <sound/initval.h>
>> @@ -88,6 +89,9 @@ struct f_midi {
>>  	int index;
>>  	char *id;
>>  	unsigned int buflen, qlen;
>> +	DECLARE_KFIFO_PTR(in_req_fifo, struct usb_request *);
>> +	unsigned int in_req_num;
>> +	unsigned int in_last_port;
>>  };
>>  
>>  static inline struct f_midi *func_to_midi(struct usb_function *f)
>> @@ -95,7 +99,7 @@ static inline struct f_midi *func_to_midi(struct usb_function *f)
>>  	return container_of(f, struct f_midi, func);
>>  }
>>  
>> -static void f_midi_transmit(struct f_midi *midi, struct usb_request *req);
>> +static void f_midi_transmit(struct f_midi *midi);
>>  
>>  DECLARE_UAC_AC_HEADER_DESCRIPTOR(1);
>>  DECLARE_USB_MIDI_OUT_JACK_DESCRIPTOR(1);
>> @@ -253,7 +257,8 @@ f_midi_complete(struct usb_ep *ep, struct usb_request *req)
>>  		} else if (ep == midi->in_ep) {
>>  			/* Our transmit completed. See if there's more to go.
>>  			 * f_midi_transmit eats req, don't queue it again. */
>> -			f_midi_transmit(midi, req);
>> +			req->length = 0;
>> +			f_midi_transmit(midi);
>>  			return;
>>  		}
>>  		break;
>> @@ -264,10 +269,12 @@ f_midi_complete(struct usb_ep *ep, struct usb_request *req)
>>  	case -ESHUTDOWN:	/* disconnect from host */
>>  		VDBG(cdev, "%s gone (%d), %d/%d\n", ep->name, status,
>>  				req->actual, req->length);
>> -		if (ep == midi->out_ep)
>> +		if (ep == midi->out_ep) {
>>  			f_midi_handle_out_data(ep, req);
>> -
>> -		free_ep_req(ep, req);
>> +			/* We don't need to free IN requests because it's handled
>> +			 * by the midi->in_req_fifo. */
>> +			free_ep_req(ep, req);
>> +		}
>>  		return;
>>  
>>  	case -EOVERFLOW:	/* buffer overrun on read means that
>> @@ -334,6 +341,21 @@ static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>>  	if (err)
>>  		return err;
>>  
>> +	/* pre-allocate write usb requests to use on f_midi_transmit. */
>> +	while (kfifo_avail(&midi->in_req_fifo)) {
>> +		struct usb_request *req =
>> +			midi_alloc_ep_req(midi->in_ep, midi->buflen);
>> +
>> +		if (req == NULL)
>> +			return -ENOMEM;
> 
> We need to free previously allocated requests in case of failure.
> 
>> +
>> +		req->length = 0;
>> +		req->complete = f_midi_complete;
>> +
>> +		kfifo_put(&midi->in_req_fifo, req);
>> +		midi->in_req_num++;
>> +	}
>> +
>>  	/* allocate a bunch of read buffers and queue them all at once. */
>>  	for (i = 0; i < midi->qlen && err == 0; i++) {
>>  		struct usb_request *req =
>> @@ -366,6 +388,20 @@ static void f_midi_disable(struct usb_function *f)
>>  	 */
>>  	usb_ep_disable(midi->in_ep);
>>  	usb_ep_disable(midi->out_ep);
>> +
>> +	/* release IN requests */
>> +	while (!kfifo_is_empty(&midi->in_req_fifo)) {
>> +		struct usb_request *req = NULL;
>> +		unsigned int len;
>> +
>> +		len = kfifo_get(&midi->in_req_fifo, &req);
>> +		if (len == 1)
>> +			free_ep_req(midi->in_ep, req);
>> +		else
>> +			ERROR(midi, "%s couldn't free usb request: something went wrong with kfifo\n",
>> +			      midi->in_ep->name);
>> +	}
>> +	midi->in_req_num = 0;
>>  }
>>  
>>  static int f_midi_snd_free(struct snd_device *device)
>> @@ -487,57 +523,111 @@ static void f_midi_transmit_byte(struct usb_request *req,
>>  	}
>>  }
>>  
>> -static void f_midi_transmit(struct f_midi *midi, struct usb_request *req)
>> +static void f_midi_drop_out_substreams(struct f_midi *midi)
>>  {
>> -	struct usb_ep *ep = midi->in_ep;
>> -	int i;
>> -
>> -	if (!ep)
>> -		return;
>> -
>> -	if (!req)
>> -		req = midi_alloc_ep_req(ep, midi->buflen);
>> -
>> -	if (!req) {
>> -		ERROR(midi, "%s: alloc_ep_request failed\n", __func__);
>> -		return;
>> -	}
>> -	req->length = 0;
>> -	req->complete = f_midi_complete;
>> +	unsigned int i;
>>  
>>  	for (i = 0; i < MAX_PORTS; i++) {
>>  		struct gmidi_in_port *port = midi->in_port[i];
>>  		struct snd_rawmidi_substream *substream = midi->in_substream[i];
>>  
>> -		if (!port || !port->active || !substream)
>> +		if (!port)
>> +			break;
>> +
>> +		if (!port->active || !substream)
>>  			continue;
>>  
>> -		while (req->length + 3 < midi->buflen) {
>> -			uint8_t b;
>> -			if (snd_rawmidi_transmit(substream, &b, 1) != 1) {
>> -				port->active = 0;
>> +		snd_rawmidi_drop_output(substream);
>> +	}
>> +}
>> +
>> +static void f_midi_transmit(struct f_midi *midi)
>> +{
>> +	struct usb_ep *ep = midi->in_ep;
>> +	bool active;
>> +
>> +	/* We only care about USB requests if IN endpoint is enabled */
>> +	if (!ep || !ep->enabled)
>> +		goto drop_out;
>> +
>> +	do {
>> +		struct usb_request *req = NULL;
>> +		unsigned int len, i;
>> +
>> +		active = false;
>> +
>> +		/* We peek the request in order to reuse it if it fails
>> +		 * to enqueue on its endpoint */
>> +		len = kfifo_peek(&midi->in_req_fifo, &req);
>> +		if (len != 1) {
>> +			ERROR(midi, "%s: Couldn't get usb request\n", __func__);
>> +			goto drop_out;
>> +		}
>> +
>> +		if (req->length > 0) {
>> +			WARNING(midi, "%s: All USB requests have been used. Current queue size "
>> +				"is %u, consider increasing it.\n", __func__, midi->in_req_num);
>> +			goto drop_out;
>> +		}
>> +
>> +		for (i = midi->in_last_port; i < MAX_PORTS; i++) {
>> +			struct gmidi_in_port *port = midi->in_port[i];
>> +			struct snd_rawmidi_substream *substream = midi->in_substream[i];
>> +
>> +			if (!port) {
>> +				/* Reset counter when we reach the last available port */
>> +				midi->in_last_port = 0;
>> +				break;
>> +			}
>> +
>> +			if (!port->active || !substream)
>> +				continue;
>> +
>> +			while (req->length + 3 < midi->buflen) {
>> +				uint8_t b;
>> +
>> +				if (snd_rawmidi_transmit(substream, &b, 1) != 1) {
>> +					port->active = 0;
>> +					break;
>> +				}
>> +				f_midi_transmit_byte(req, port, b);
>> +			}
>> +
>> +			active = !!port->active;
>> +			/* Check if last port is still active, which means that
>> +			 * there is still data on that substream but this current
>> +			 * request run out of space. */
>> +			if (active) {
>> +				midi->in_last_port = i;
>> +				/* There is no need to re-iterate though midi ports. */
>>  				break;
>>  			}
>> -			f_midi_transmit_byte(req, port, b);
>>  		}
>> -	}
>>  
>> -	if (req->length > 0 && ep->enabled) {
>> -		int err;
>> +		if (req->length > 0) {
>> +			int err;
>>  
>> -		err = usb_ep_queue(ep, req, GFP_ATOMIC);
>> -		if (err < 0)
>> -			ERROR(midi, "%s queue req: %d\n",
>> -			      midi->in_ep->name, err);
>> -	} else {
>> -		free_ep_req(ep, req);
>> -	}
>> +			err = usb_ep_queue(ep, req, GFP_ATOMIC);
>> +			if (err < 0) {
>> +				ERROR(midi, "%s failed to queue req: %d\n",
>> +				      midi->in_ep->name, err);
>> +				req->length = 0; /* Re-use request next time. */
>> +			} else {
>> +				/* Upon success, put request at the back of the queue. */
>> +				kfifo_skip(&midi->in_req_fifo);
>> +				kfifo_put(&midi->in_req_fifo, req);
> 
> There are simpler and clearer ways to implement cyclic buffer than using
> kfifo. To be honest, it took ma a while to realize what's going on. As
> long as you mark unused requests by setting req->length to zero you only
> need to store index of last used req to be able to achieve the same effect.

That is true but that's exactly what I am trying to avoid here. I didn't
want to add a counter and deal with counter++ and counter-- all the
time. kfifo is fast and has a clean and nice interface to deal with that.

I can write a comment right next to it just to make things clearer.

> 
>> +			}
>> +		}
>> +	} while (active);
>> +
>> +drop_out:
>> +	f_midi_drop_out_substreams(midi);
>>  }
>>  
>>  static void f_midi_in_tasklet(unsigned long data)
>>  {
>>  	struct f_midi *midi = (struct f_midi *) data;
>> -	f_midi_transmit(midi, NULL);
>> +	f_midi_transmit(midi);
>>  }
>>  
>>  static int f_midi_in_open(struct snd_rawmidi_substream *substream)
>> @@ -663,6 +753,7 @@ static int f_midi_register_card(struct f_midi *midi)
>>  		goto fail;
>>  	}
>>  	midi->rmidi = rmidi;
>> +	midi->in_last_port = 0;
>>  	strcpy(rmidi->name, card->shortname);
>>  	rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
>>  			    SNDRV_RAWMIDI_INFO_INPUT |
>> @@ -1057,6 +1148,7 @@ static void f_midi_free(struct usb_function *f)
>>  	mutex_lock(&opts->lock);
>>  	for (i = opts->in_ports - 1; i >= 0; --i)
>>  		kfree(midi->in_port[i]);
>> +	kfifo_free(&midi->in_req_fifo);
>>  	kfree(midi);
>>  	--opts->refcnt;
>>  	mutex_unlock(&opts->lock);
>> @@ -1130,6 +1222,12 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
>>  	midi->index = opts->index;
>>  	midi->buflen = opts->buflen;
>>  	midi->qlen = opts->qlen;
>> +	midi->in_req_num = 0;
>> +	midi->in_last_port = 0;
>> +
>> +	if (kfifo_alloc(&midi->in_req_fifo, midi->qlen, GFP_KERNEL))
>> +		goto setup_fail;
>> +
>>  	++opts->refcnt;
>>  	mutex_unlock(&opts->lock);
>>  
>> diff --git a/drivers/usb/gadget/legacy/gmidi.c b/drivers/usb/gadget/legacy/gmidi.c
>> index be8e91d..f68c188 100644
>> --- a/drivers/usb/gadget/legacy/gmidi.c
>> +++ b/drivers/usb/gadget/legacy/gmidi.c
>> @@ -53,7 +53,7 @@ MODULE_PARM_DESC(buflen, "MIDI buffer length");
>>  
>>  static unsigned int qlen = 32;
>>  module_param(qlen, uint, S_IRUGO);
>> -MODULE_PARM_DESC(qlen, "USB read request queue length");
>> +MODULE_PARM_DESC(qlen, "USB read and write request queue length");
>>  
>>  static unsigned int in_ports = 1;
>>  module_param(in_ports, uint, S_IRUGO);
>>
> 
> Best regards,
> Robert
> 


Felipe

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