From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NydCY-0000h9-2V for qemu-devel@nongnu.org; Sun, 04 Apr 2010 23:42:14 -0400 Received: from [140.186.70.92] (port=58074 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NydCR-0000h1-6F for qemu-devel@nongnu.org; Sun, 04 Apr 2010 23:42:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1NydCQ-0005oE-09 for qemu-devel@nongnu.org; Sun, 04 Apr 2010 23:42:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11191) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1NydCP-0005o5-Os for qemu-devel@nongnu.org; Sun, 04 Apr 2010 23:42:05 -0400 Date: Mon, 5 Apr 2010 09:10:21 +0530 From: Amit Shah Subject: Re: [Qemu-devel] [PATCH 3/6] Make char muxer more robust wrt small FIFOs Message-ID: <20100405034021.GA7100@amit-x200.redhat.com> References: <1270140161-17216-1-git-send-email-agraf@suse.de> <1270140161-17216-4-git-send-email-agraf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1270140161-17216-4-git-send-email-agraf@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 (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. > 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? Amit