From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NzWIg-0004MC-6U for qemu-devel@nongnu.org; Wed, 07 Apr 2010 10:32:14 -0400 Received: from [140.186.70.92] (port=40933 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NzWIa-0004LH-Es for qemu-devel@nongnu.org; Wed, 07 Apr 2010 10:32:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1NzWIZ-000688-3J for qemu-devel@nongnu.org; Wed, 07 Apr 2010 10:32:08 -0400 Received: from cantor2.suse.de ([195.135.220.15]:34258 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1NzWIY-000682-RU for qemu-devel@nongnu.org; Wed, 07 Apr 2010 10:32:07 -0400 Message-ID: <4BBC9764.1080402@suse.de> Date: Wed, 07 Apr 2010 16:32:04 +0200 From: Alexander Graf MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 3/6] Make char muxer more robust wrt small FIFOs 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> In-Reply-To: <20100405034021.GA7100@amit-x200.redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Amit Shah Cc: waldi@debian.org, Carsten Otte , qemu-devel@nongnu.org, aurelien@aurel32.net 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 :-). Alex