Re: [PATCH v3][uqmaster] kvm: Flush coalesced MMIO buffer periodly

From: Marcelo Tosatti <mtosatti@redhat.com>
To: Sheng Yang <sheng@linux.intel.com>
Cc: Avi Kivity <avi@redhat.com>,
	Anthony Liguori <anthony@codemonkey.ws>,
	Alexander Graf <agraf@suse.de>,
	kvm@vger.kernel.org, qemu-devel@nongnu.org
Subject: Re: [PATCH v3][uqmaster] kvm: Flush coalesced MMIO buffer periodly
Date: Tue, 26 Jan 2010 10:43:04 -0200	[thread overview]
Message-ID: <20100126124304.GB25128@amt.cnet> (raw)
In-Reply-To: <1264504876-24493-1-git-send-email-sheng@linux.intel.com>

On Tue, Jan 26, 2010 at 07:21:16PM +0800, Sheng Yang wrote:
> The default action of coalesced MMIO is, cache the writing in buffer, until:
> 1. The buffer is full.
> 2. Or the exit to QEmu due to other reasons.
> 
> But this would result in a very late writing in some condition.
> 1. The each time write to MMIO content is small.
> 2. The writing interval is big.
> 3. No need for input or accessing other devices frequently.
> 
> This issue was observed in a experimental embbed system. The test image
> simply print "test" every 1 seconds. The output in QEmu meets expectation,
> but the output in KVM is delayed for seconds.
> 
> Per Avi's suggestion, I hooked flushing coalesced MMIO buffer in VGA update
> handler. By this way, We don't need vcpu explicit exit to QEmu to
> handle this issue.
> 
> Signed-off-by: Sheng Yang <sheng@linux.intel.com>

Applied, thanks.