From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [203.10.76.45]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mx.ozlabs.org", Issuer "CA Cert Signing Authority" (verified OK)) by bilbo.ozlabs.org (Postfix) with ESMTPS id 32751B6F31 for ; Thu, 27 Aug 2009 16:53:21 +1000 (EST) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by ozlabs.org (Postfix) with ESMTP id 397BEDDD01 for ; Thu, 27 Aug 2009 16:53:20 +1000 (EST) Date: Thu, 27 Aug 2009 12:22:51 +0530 From: Amit Shah To: Michael Ellerman Subject: Re: Extending virtio_console to support multiple ports Message-ID: <20090827065251.GB3218@amit-x200.redhat.com> References: <1251181044-3696-1-git-send-email-amit.shah@redhat.com> <20090826112718.GA11117@amit-x200.redhat.com> <20090826154552.GA31910@amit-x200.redhat.com> <1251349485.6267.6.camel@concordia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1251349485.6267.6.camel@concordia> Cc: kvm@vger.kernel.org, linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, miltonm@bga.com, qemu-devel@nongnu.org, borntraeger@de.ibm.com, brueckner@linux.vnet.ibm.com, virtualization@lists.linux-foundation.org, alan@linux.intel.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On (Thu) Aug 27 2009 [15:04:45], Michael Ellerman wrote: > On Wed, 2009-08-26 at 21:15 +0530, Amit Shah wrote: > > [cc'ing some people who have made some commits in hvc_console.c] > > > > On (Wed) Aug 26 2009 [16:57:18], Amit Shah wrote: > > > On (Tue) Aug 25 2009 [11:47:20], Amit Shah wrote: > > > > > > > > Hello all, > > > > > > > > Here is a new iteration of the patch series that implements a > > > > transport for guest and host communications. > > > > > > > > The code has been updated to reuse the virtio-console device instead > > > > of creating a new virtio-serial device. > > > > > > And the problem now is that hvc calls the put_chars function with > > > spinlocks held and we now allocate pages in send_buf(), called from > > > put_chars. > > > > > > A few solutions: > > > > [snip] > > > > > - Convert hvc's usage of spinlocks to mutexes. I've no idea how this > > > will play out; I'm no expert here. But I did try doing this and so far > > > it all looks OK. No lockups, lockdep warnings, nothing. I have full > > > debugging enabled. But this doesn't mean it's right. > > > > So just to test this further I added the capability to have more than > > one hvc console spawn from virtio_console, created two consoles and did > > a 'cat' of a file in each of the virtio-consoles. It's been running for > > half an hour now without any badness. No spew in debug logs too. > > > > I also checked the code in hvc_console.c that takes the spin_locks. > > Nothing there that runs from (or needs to run from) interrupt context. > > So the change to mutexes does seem reasonable. Also, the spinlock code > > was added really long back -- git blame shows Linus' first git commit > > introduced them in the git history, so it's pure legacy baggage. > > I won't tell Ryan you called his code "pure legacy baggage" if you > don't ;) > > http://git.kernel.org/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=commitdiff;h=d450b4ae023fb4be175389c18f4f87677da03020 Thanks for the link! (and this general area might be the one that doesn't get major upheavals in 5-yr spans :-) Amit