Re: [PATCH v3] usb: gadget: u_serial: improve performance for large data

From: Felipe Balbi <balbi@kernel.org>
To: "Macpaul Lin" <macpaul.lin@mediatek.com>,
	"Alan Stern" <stern@rowland.harvard.edu>,
	"Chunfeng Yun" <chunfeng.yun@mediatek.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"Michał Mirosław" <mirq-linux@rere.qmqm.pl>,
	"Sergey Organov" <sorganov@gmail.com>,
	"Fabrice Gasnier" <fabrice.gasnier@st.com>,
	linux-usb@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org
Cc: Macpaul Lin <macpaul.lin@gmail.com>,
	Macpaul Lin <macpaul.lin@mediatek.com>,
	Mediatek WSD Upstream <wsd_upstream@mediatek.com>
Subject: Re: [PATCH v3] usb: gadget: u_serial: improve performance for large data
Date: Wed, 24 Jun 2020 09:50:27 +0300	[thread overview]
Message-ID: <87r1u5vtxo.fsf@kernel.org> (raw)
In-Reply-To: <1592372577-7986-1-git-send-email-macpaul.lin@mediatek.com>

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Hi,

Macpaul Lin <macpaul.lin@mediatek.com> writes:
> Nowadays some embedded systems use VCOM to transfer large log and data.
> Take LTE MODEM as an example, during the long debugging stage, large
> log and data were transfer through VCOM when doing field try or in
> operator's lab. Here we suggest slightly increase the transfer buffer
> in u_serial.c for performance improving.
>
> Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
> ---
> Changes for v2:
>   - Drop previous patch for adding flag which indicates hardware capability in
>     gadget.h and in DMA engine according to Alan's suggestion. Thanks.
>   - Replace requested buffer size "REQ_BUF_SIZE" instead of checking hardware
>     capability.
>   - Refine commit messages.
> Changes for v3:
>   - Code: no change.
>     Commit: Add missing change log in v2.
>
>  drivers/usb/gadget/function/u_serial.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index 3cfc6e2..d7912a9 100644
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -80,6 +80,7 @@
>  #define QUEUE_SIZE		16
>  #define WRITE_BUF_SIZE		8192		/* TX only */
>  #define GS_CONSOLE_BUF_SIZE	8192
> +#define REQ_BUF_SIZE		4096
>  
>  /* console info */
>  struct gs_console {
> @@ -247,7 +248,7 @@ static int gs_start_tx(struct gs_port *port)
>  			break;
>  
>  		req = list_entry(pool->next, struct usb_request, list);
> -		len = gs_send_packet(port, req->buf, in->maxpacket);
> +		len = gs_send_packet(port, req->buf, REQ_BUF_SIZE);
>  		if (len == 0) {
>  			wake_up_interruptible(&port->drain_wait);
>  			break;
> @@ -514,7 +515,7 @@ static int gs_alloc_requests(struct usb_ep *ep, struct list_head *head,
>  	 * be as speedy as we might otherwise be.
>  	 */
>  	for (i = 0; i < n; i++) {
> -		req = gs_alloc_req(ep, ep->maxpacket, GFP_ATOMIC);
> +		req = gs_alloc_req(ep, REQ_BUF_SIZE, GFP_ATOMIC);

since this can only be applied for the next merge window, it would be
much better if you work rework how requests are used here and, as I
mentioned in the other subthread, preallocate a list of requests that
get recycled. This would allow us to allocate memory without GFP_ATOMIC.

-- 
balbi

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