lkml.org 
[lkml]   [2009]   [Aug]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: Extending virtio_console to support multiple ports
From
Date
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


cheers
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2009-08-27 07:07    [W:0.081 / U:0.104 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site