From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NzWVh-0000EV-4c for qemu-devel@nongnu.org; Wed, 07 Apr 2010 10:45:41 -0400 Received: from [140.186.70.92] (port=46416 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NzWVf-0000DX-Ll for qemu-devel@nongnu.org; Wed, 07 Apr 2010 10:45:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1NzWVd-0007S2-Sx for qemu-devel@nongnu.org; Wed, 07 Apr 2010 10:45:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38860) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1NzWVd-0007Rx-JR for qemu-devel@nongnu.org; Wed, 07 Apr 2010 10:45:37 -0400 Date: Wed, 7 Apr 2010 20:13:52 +0530 From: Amit Shah Subject: Re: [Qemu-devel] [PATCH 3/6] Make char muxer more robust wrt small FIFOs Message-ID: <20100407144351.GV4135@amit-x200.redhat.com> References: <1270140161-17216-1-git-send-email-agraf@suse.de> <1270140161-17216-4-git-send-email-agraf@suse.de> <20100405034021.GA7100@amit-x200.redhat.com> <4BBC9764.1080402@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BBC9764.1080402@suse.de> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: waldi@debian.org, Carsten Otte , qemu-devel@nongnu.org, aurelien@aurel32.net On (Wed) Apr 07 2010 [16:32:04], Alexander Graf wrote: > Amit Shah wrote: > > On (Thu) Apr 01 2010 [18:42:38], Alexander Graf wrote: > > > >> Virtio-Console can only process one character at a time. > >> > > > > The host can process as many as you give it, depending on the buffer > > size exposed by the guest. > > > > On older guests (guest kernels w/o multiport support), the guest reads > > input from host, processes it and only then opens up another buffer for > > the host to write into. > > > > On newer guests (guest kernels that support multiport), the guest > > fills the entire vq so that host can send as many buffers as possible > > without getting throttled. I guess you're getting hit by this. > > > > Probably, yes. > > >> Using it on S390 > >> gave me strage "lags" where I got the character I pressed before when > >> pressing one. So I typed in "abc" and only received "a", then pressed "d" > >> but the guest received "b" and so on. > >> > > > > This might be because qemu-char would not be able to send out 'b' while > > the guest still processes 'a' and has no free buffers to write out to. > > On seeing 'd', it flushes its queue. > > > > Can you try using a 2.6.34-rc3 kernel without this patch to see if > > things work fine? > > > > Hrm - would it actually matter? We need to have older guest kernels > working anyways. And my S390 LPAR doesn't exactly have a lot of disk > space, so compiling a kernel is anything but fun :-). Oh I just want to find out if it works for you -- you shouldn't get hit by the 1-char limit anymore. Amit -- http://log.amitshah.net/