From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757468AbbIDEUm (ORCPT ); Fri, 4 Sep 2015 00:20:42 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:59303 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753458AbbIDEUk (ORCPT ); Fri, 4 Sep 2015 00:20:40 -0400 Date: Thu, 3 Sep 2015 21:20:39 -0700 From: Greg Kroah-Hartman To: Vitaly Kuznetsov Cc: Jiri Slaby , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, "K. Y. Srinivasan" , Dexuan Cui Subject: Re: [PATCH] serial: core: prevent softlockups on slow consoles Message-ID: <20150904042039.GA3719@kroah.com> References: <1441031656-17959-1-git-send-email-vkuznets@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1441031656-17959-1-git-send-email-vkuznets@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 31, 2015 at 04:34:16PM +0200, Vitaly Kuznetsov wrote: > Hyper-V serial port is very slow on multi-vCPU guest, this causes > soflockups on intensive console writes. Touch nmi watchdog after putting > every char on port to avoid the issue for all serial drivers, the overhead > should be small. > > This is just a part of the fix: serial8250_console_write() disables irqs > for all its execution time (which on such slow consoles can be dozens of > seconds), it should be possible to observe devices being stuck on this > CPU. We need to find a better way, e.g. do output in batches enabling irqs > in between. > > Signed-off-by: Vitaly Kuznetsov > --- > drivers/tty/serial/serial_core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > index f368520..cc05785 100644 > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -33,7 +33,7 @@ > #include /* for serial_state and serial_icounter_struct */ > #include > #include > -#include > +#include > > #include > #include > @@ -1792,6 +1792,7 @@ void uart_console_write(struct uart_port *port, const char *s, > if (*s == '\n') > putchar(port, '\r'); > putchar(port, *s); > + touch_nmi_watchdog(); I don't like this, please narrow this down to the real problem that your hardware has here, the putchar function should not be this slow. If it is, something is wrong. greg k-h