Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754440Ab1DDVhJ (ORCPT ); Mon, 4 Apr 2011 17:37:09 -0400 Received: from mail-iy0-f174.google.com ([209.85.210.174]:43068 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752860Ab1DDVhE (ORCPT ); Mon, 4 Apr 2011 17:37:04 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=VXQ7Qrhv/F9XW4tb2J4XsnIVUpMUQiCLDsPKo4SzFaz5UAgpEoTq5UUB9PTXWJ2K7n na0/BBAK2mBzqm4ig4e7QdofhcyngOnS5ncfR99LfTEU/2xFExKiKyxtoYCzJqpPCrE7 XZFHtarSrYl9CugwD1gdVRNGx6d8eTKNdTSzU= Date: Mon, 4 Apr 2011 14:36:59 -0700 From: Dmitry Torokhov To: Jeff Brown Cc: rydberg@euromail.se, djkurtz@google.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/4] input: evdev: Make device readable only when it contains a complete packet. Message-ID: <20110404213659.GC984@core.coreip.homeip.net> References: <1301727259-5185-1-git-send-email-jeffbrown@android.com> <1301727259-5185-4-git-send-email-jeffbrown@android.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1301727259-5185-4-git-send-email-jeffbrown@android.com> 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: 3312 Lines: 98 On Fri, Apr 01, 2011 at 11:54:19PM -0700, Jeff Brown wrote: > This patch modifies evdev so that it only becomes readable when > the buffer contains an EV_SYN event other than SYN_MT_REPORT. I think we should target SYN_REPORT directly. SYN_CONFIG is unused and SYN_DROPPED is not interesting till next SYN_REPORT anyway. Given the changes to the previous patch I have the following: Input: evdev - only signal polls on full packets From: Jeff Brown This patch modifies evdev so that it only becomes readable when the buffer contains an EV_SYN/SYN_REPORT event. On SMP systems, it is possible for an evdev client blocked on poll() to wake up and read events from the evdev ring buffer at the same rate as they are enqueued. This can result in high CPU usage, particularly for MT devices, because the client ends up reading events one at a time instead of reading complete packets. We eliminate this problem by making the device readable only when the buffer contains at least one complete packet. This causes clients to block until the entire packet is available. Signed-off-by: Jeff Brown Signed-off-by: Dmitry Torokhov --- drivers/input/evdev.c | 13 +++++++++---- 1 files changed, 9 insertions(+), 4 deletions(-) diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c index f1c0910..5398761 100644 --- a/drivers/input/evdev.c +++ b/drivers/input/evdev.c @@ -41,6 +41,7 @@ struct evdev { struct evdev_client { unsigned int head; unsigned int tail; + unsigned int last_syn; /* position of the last EV_SYN/SYN_REPORT */ spinlock_t buffer_lock; /* protects access to buffer, head and tail */ struct fasync_struct *fasync; struct evdev *evdev; @@ -72,12 +73,16 @@ static void evdev_pass_event(struct evdev_client *client, client->buffer[client->tail].type = EV_SYN; client->buffer[client->tail].code = SYN_DROPPED; client->buffer[client->tail].value = 0; + + client->last_syn = client->tail; } spin_unlock(&client->buffer_lock); - if (event->type == EV_SYN) + if (event->type == EV_SYN && event->code == SYN_REPORT) { + client->last_syn = client->head; kill_fasync(&client->fasync, SIGIO, POLL_IN); + } } /* @@ -387,12 +392,12 @@ static ssize_t evdev_read(struct file *file, char __user *buffer, if (count < input_event_size()) return -EINVAL; - if (client->head == client->tail && evdev->exist && + if (client->last_syn == client->tail && evdev->exist && (file->f_flags & O_NONBLOCK)) return -EAGAIN; retval = wait_event_interruptible(evdev->wait, - client->head != client->tail || !evdev->exist); + client->last_syn != client->tail || !evdev->exist); if (retval) return retval; @@ -421,7 +426,7 @@ static unsigned int evdev_poll(struct file *file, poll_table *wait) poll_wait(file, &evdev->wait, wait); mask = evdev->exist ? POLLOUT | POLLWRNORM : POLLHUP | POLLERR; - if (client->head != client->tail) + if (client->last_syn != client->tail) mask |= POLLIN | POLLRDNORM; return mask; Thanks. -- Dmitry -- 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/