Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933550Ab3ECQkm (ORCPT ); Fri, 3 May 2013 12:40:42 -0400 Received: from smtp1.mail.ru ([94.100.176.129]:50206 "EHLO smtp1.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760490Ab3ECQkl (ORCPT ); Fri, 3 May 2013 12:40:41 -0400 Message-ID: <5183F62A.1020801@list.ru> Date: Fri, 03 May 2013 21:38:50 +0400 From: Stas Sergeev User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 MIME-Version: 1.0 To: Greg KH CC: Jarkko Huijts , Alan Cox , linux-usb@vger.kernel.org, linux-serial@vger.kernel.org, Linux kernel , Caylan Van Larson , "Rafael J. Wysocki" Subject: Re: Regression: ftdi_sio is slow (since Wed Oct 10 15:05:06 2012) References: <5183D196.2080305@list.ru> <20130503163008.GA30699@kroah.com> In-Reply-To: <20130503163008.GA30699@kroah.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam: Not detected X-Mras: Ok Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1344 Lines: 34 03.05.2013 20:30, Greg KH пишет: > We need some way to check the chars in the buffer, is the device you are > using just very slow to respond to this request? How slow? Do you have > a test case that we can see how it is affected? Greg, unfortunately, I do have nothing. The customer is in CC list, so maybe he will provide the test-case, but I doubt. Please, what are your concerns here? The patch in question does this: --- + ret = usb_control_msg(port->serial->dev, + usb_rcvctrlpipe(port->serial->dev, 0), + FTDI_SIO_GET_MODEM_STATUS_REQUEST, + FTDI_SIO_GET_MODEM_STATUS_REQUEST_TYPE, + 0, priv->interface, + buf, 2, WDR_TIMEOUT); --- Obviously, this is too expensive to call too frequently, or am I missing something? I asked the customer to comment out tty_chars_in_buffer(tty) < WAKEUP_CHARS line in n_tty.c, and he said that cured his problems, so I think my guess was right. The patch claims it only affects tcdrain() and close(). Its trivial to see it also affects poll(), select() and TIOCOUTQ ioctl, so even from that it is already broken. Why do you need a test-case for this? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/