From patchwork Wed Jul 27 16:55:20 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Denis V. Lunev" X-Patchwork-Id: 9250175 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id B2F62607F0 for ; Wed, 27 Jul 2016 16:56:02 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A53331FE6A for ; Wed, 27 Jul 2016 16:56:02 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 9A09C26907; Wed, 27 Jul 2016 16:56:02 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id EC2E41FE6A for ; Wed, 27 Jul 2016 16:56:01 +0000 (UTC) Received: from localhost ([::1]:47731 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bSS7k-0006BO-0B for patchwork-qemu-devel@patchwork.kernel.org; Wed, 27 Jul 2016 12:56:00 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35048) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bSS7N-00069V-EQ for qemu-devel@nongnu.org; Wed, 27 Jul 2016 12:55:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bSS7J-0004eF-Ln for qemu-devel@nongnu.org; Wed, 27 Jul 2016 12:55:36 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:15729 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bSS7J-0004dC-8o for qemu-devel@nongnu.org; Wed, 27 Jul 2016 12:55:33 -0400 Received: from hades.sw.ru ([10.30.8.132]) by relay.sw.ru (8.13.4/8.13.4) with ESMTP id u6QE4hsE030220; Tue, 26 Jul 2016 17:04:43 +0300 (MSK) From: "Denis V. Lunev" To: qemu-devel@nongnu.org Date: Wed, 27 Jul 2016 19:55:20 +0300 Message-Id: <1469638520-32706-1-git-send-email-den@openvz.org> X-Mailer: git-send-email 2.5.0 X-detected-operating-system: by eggs.gnu.org: OpenBSD 3.x X-Received-From: 195.214.232.25 Subject: [Qemu-devel] [PATCH 1/1] ehci: faster frame index calculation for skipped frames X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: den@openvz.org, Evgeny Yakovlev , Gerd Hoffmann Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Evgeny Yakovlev ehci_update_frindex takes time linearly proportional to a number of uframes to calculate new frame index and raise FLR interrupts, which is a problem for large amounts of uframes. If we experience large delays between echi timer callbacks (i.e. because other periodic handlers have taken a lot of time to complete) we get a lot of skipped frames which then delay ehci timer callback more and this leads to deadlocking the system when ehci schedules next callback to be too soon. Observable behaviour is qemu consuming 100% host CPU time while guest is unresponsive. This misbehavior could happen for a while and QEMU does not get out from this state automatically without the patch. This change makes ehci_update_frindex execute in constant time. Signed-off-by: Evgeny Yakovlev Signed-off-by: Denis V. Lunev CC: Gerd Hoffmann --- hw/usb/hcd-ehci.c | 31 +++++++++++++++---------------- 1 file changed, 15 insertions(+), 16 deletions(-) diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c index 43a8f7a..b093db7 100644 --- a/hw/usb/hcd-ehci.c +++ b/hw/usb/hcd-ehci.c @@ -2206,29 +2206,28 @@ static void ehci_advance_periodic_state(EHCIState *ehci) static void ehci_update_frindex(EHCIState *ehci, int uframes) { - int i; - if (!ehci_enabled(ehci) && ehci->pstate == EST_INACTIVE) { return; } - for (i = 0; i < uframes; i++) { - ehci->frindex++; - - if (ehci->frindex == 0x00002000) { - ehci_raise_irq(ehci, USBSTS_FLR); - } + /* Generate FLR interrupt if frame index rolls over 0x2000 */ + if ((ehci->frindex % 0x2000) + uframes >= 0x2000) { + ehci_raise_irq(ehci, USBSTS_FLR); + } - if (ehci->frindex == 0x00004000) { - ehci_raise_irq(ehci, USBSTS_FLR); - ehci->frindex = 0; - if (ehci->usbsts_frindex >= 0x00004000) { - ehci->usbsts_frindex -= 0x00004000; - } else { - ehci->usbsts_frindex = 0; - } + /* How many times will frindex roll over 0x4000 with this frame count? + * usbsts_frindex is decremented by 0x4000 on rollover until it reaches 0 + */ + int rollovers = (ehci->frindex + uframes) / 0x4000; + if (rollovers > 0) { + if (ehci->usbsts_frindex >= (rollovers * 0x4000)) { + ehci->usbsts_frindex -= 0x4000 * rollovers; + } else { + ehci->usbsts_frindex = 0; } } + + ehci->frindex = (ehci->frindex + uframes) % 0x4000; } static void ehci_frame_timer(void *opaque)