Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933545Ab3ECQcd (ORCPT ); Fri, 3 May 2013 12:32:33 -0400 Received: from mail-da0-f47.google.com ([209.85.210.47]:44794 "EHLO mail-da0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760550Ab3ECQca (ORCPT ); Fri, 3 May 2013 12:32:30 -0400 Date: Fri, 3 May 2013 09:30:08 -0700 From: Greg KH To: Stas Sergeev 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) Message-ID: <20130503163008.GA30699@kroah.com> References: <5183D196.2080305@list.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5183D196.2080305@list.ru> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1282 Lines: 35 On Fri, May 03, 2013 at 07:02:46PM +0400, Stas Sergeev wrote: > Hi. > > We have a regression because of this patch: > http://lkml.indiana.edu/hypermail/linux/kernel/1210.1/01456.html > While it is arguably reasonable to have this for tcdrain or close, > it also slows down poll/select a lot because n_tty_poll() does this: > > tty_chars_in_buffer(tty) < WAKEUP_CHARS What do you mean "slows down"? > And it also slows down TIOCOUTQ ioctl I think (not measured). > The slowdown of select() is big, the customer reports the inability > to work that way. Inability to work what way? > Is this patch really needed? I mean, if the time to check TEMT is > longer than to xmit that char, then what's the use? > Or, if it is really a big deal, I guess it would be necessary to add > a separate, .chars_in_buffer_fast method. 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? thanks, greg k-h -- 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/