From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=49907 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PezIm-0002gi-Ba for qemu-devel@nongnu.org; Mon, 17 Jan 2011 19:20:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PezIh-0006WC-75 for qemu-devel@nongnu.org; Mon, 17 Jan 2011 19:20:00 -0500 Received: from mail-ey0-f173.google.com ([209.85.215.173]:50274) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PezIg-0006W6-TD for qemu-devel@nongnu.org; Mon, 17 Jan 2011 19:19:55 -0500 Received: by eyg7 with SMTP id 7so3126346eyg.4 for ; Mon, 17 Jan 2011 16:19:54 -0800 (PST) Date: Tue, 18 Jan 2011 01:19:50 +0100 From: "Edgar E. Iglesias" Message-ID: <20110118001950.GA11802@laped.lan> References: <20110117100308.GA12308@edde.se.axis.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110117100308.GA12308@edde.se.axis.com> Subject: [Qemu-devel] Re: MIPS, io-thread, icount and wfi List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org On Mon, Jan 17, 2011 at 11:03:08AM +0100, Edgar E. Iglesias wrote: > Hi, > > I'm running an io-thread enabled qemu-system-mipsel with icount. > When the guest (linux) goes to sleep through the wait insn (waiting > to be woken up by future timer interrupts), the thing deadlocks. > > IIUC, this is because vm timers are driven by icount, but the CPU is > halted so icount makes no progress and time stands still. > > I've locally disabled vcpu halting when icount is enabled, that > works around my problem but of course makes qemu consume 100% host cpu. > > I don't know why I only see this problem with io-thread builds? > Could be related timing and luck. > > Would be interesting to know if someone has any info on how this was > intended to work (if it was)? And if there are ideas for better > workarounds or fixes that don't disable vcpu halting entirely. Hi, I've found the problem. For some reason io-thread builds use a static timeout for wait loops. The entire chunk of code that makes sure qemu_icount makes forward progress when the CPU's are idle has been ifdef'ed away... This fixes the problem for me, hopefully without affecting io-thread runs without icount. commit 0f4f3a919952500b487b438c5520f07a1c6be35b Author: Edgar E. Iglesias Date: Tue Jan 18 01:01:57 2011 +0100 qemu-timer: Fix timeout calc for io-thread with icount Make sure we always make forward progress with qemu_icount to avoid deadlocks. For io-thread, use the static 1000 timeout only if icount is disabled. Signed-off-by: Edgar E. Iglesias diff --git a/qemu-timer.c b/qemu-timer.c index 95814af..db1ec49 100644 --- a/qemu-timer.c +++ b/qemu-timer.c @@ -110,7 +110,6 @@ static int64_t cpu_get_clock(void) } } -#ifndef CONFIG_IOTHREAD static int64_t qemu_icount_delta(void) { if (!use_icount) { @@ -124,7 +123,6 @@ static int64_t qemu_icount_delta(void) return cpu_get_icount() - cpu_get_clock(); } } -#endif /* enable cpu_get_ticks() */ void cpu_enable_ticks(void) @@ -1077,9 +1075,17 @@ void quit_timers(void) int qemu_calculate_timeout(void) { -#ifndef CONFIG_IOTHREAD int timeout; +#ifdef CONFIG_IOTHREAD + /* When using icount, making forward progress with qemu_icount when the + guest CPU is idle is critical. We only use the static io-thread timeout + for non icount runs. */ + if (!use_icount) { + return 1000; + } +#endif + if (!vm_running) timeout = 5000; else { @@ -1110,8 +1116,5 @@ int qemu_calculate_timeout(void) } return timeout; -#else /* CONFIG_IOTHREAD */ - return 1000; -#endif }