From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dor Laor Subject: Set the iothread's eventfd/pipe descriptors to non-blocking Date: Fri, 17 Jul 2009 01:18:58 +0300 Message-ID: <4A5FA752.6000502@redhat.com> Reply-To: dlaor@redhat.com Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------010404060004080400000300" To: kvm-devel Return-path: Received: from mx2.redhat.com ([66.187.237.31]:40995 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751569AbZGPWSd (ORCPT ); Thu, 16 Jul 2009 18:18:33 -0400 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id n6GMIXBS011311 for ; Thu, 16 Jul 2009 18:18:33 -0400 Received: from ns3.rdu.redhat.com (ns3.rdu.redhat.com [10.11.255.199]) by int-mx2.corp.redhat.com (8.13.1/8.13.1) with ESMTP id n6GMIWSG010071 for ; Thu, 16 Jul 2009 18:18:33 -0400 Received: from localhost.localdomain (vpn-6-179.tlv.redhat.com [10.35.6.179]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id n6GMIUKK001805 for ; Thu, 16 Jul 2009 18:18:31 -0400 Sender: kvm-owner@vger.kernel.org List-ID: This is a multi-part message in MIME format. --------------010404060004080400000300 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit It replaces the previous fix of using select. --------------010404060004080400000300 Content-Type: text/plain; name="0001-Set-the-iothread-s-eventfd-pipe-descriptors-to-non-b.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename*0="0001-Set-the-iothread-s-eventfd-pipe-descriptors-to-non-b.pa"; filename*1="tch" >>From ab5ae4bb69f8ab6c9a476f7823cb8d6729d31594 Mon Sep 17 00:00:00 2001 From: Dor Laor Date: Wed, 15 Jul 2009 17:53:16 +0300 Subject: [PATCH] Set the iothread's eventfd/pipe descriptors to non-blocking. It fixes migration issue when the destination is loaded. If the migration socket is full, we get EAGAIN for the write. The set_fd_handler2 defers the write for later on. The function tries to wake up the iothread by qemu_kvm_notify_work. Since this happens in a loop, multiple times, the pipe that emulates eventfd becomes full and we get a deadlock. Mark McLoughlin suggested to remove spurious wake-up of the migration code when we get EAGAIN and wait for the socket to become writeable. (+1) Nevertheless, the pipe descriptors shouldn't be blocking and the reader can also read several chunks in a time. Signed-off-by: Dor Laor --- qemu-kvm.c | 24 ++++++++++++++---------- 1 files changed, 14 insertions(+), 10 deletions(-) diff --git a/qemu-kvm.c b/qemu-kvm.c index ed7e466..68a453c 100644 --- a/qemu-kvm.c +++ b/qemu-kvm.c @@ -2107,14 +2107,17 @@ void qemu_kvm_notify_work(void) if (len == -1 && errno == EINTR) continue; - if (len <= 0) + /* In case we have a pipe, there is not reason to insist writing + * 8 bytes + */ + if (len == -1 && errno == EAGAIN) break; + if (len <= 0) + break; + offset += len; } - - if (offset != 8) - fprintf(stderr, "failed to notify io thread\n"); } /* If we have signalfd, we mask out the signals we want to handle and then @@ -2153,20 +2156,18 @@ static void sigfd_handler(void *opaque) static void io_thread_wakeup(void *opaque) { int fd = (unsigned long)opaque; - char buffer[8]; - size_t offset = 0; + char buffer[4096]; - while (offset < 8) { + /* Drain the pipe/(eventfd) */ + while (1) { ssize_t len; - len = read(fd, buffer + offset, 8 - offset); + len = read(fd, buffer, sizeof(buffer)); if (len == -1 && errno == EINTR) continue; if (len <= 0) break; - - offset += len; } } @@ -2184,6 +2185,9 @@ int kvm_main_loop(void) return -errno; } + fcntl(fds[0], F_SETFL, O_NONBLOCK); + fcntl(fds[1], F_SETFL, O_NONBLOCK); + qemu_set_fd_handler2(fds[0], NULL, io_thread_wakeup, NULL, (void *)(unsigned long)fds[0]); -- 1.6.2.5 --------------010404060004080400000300--