On Tue, Feb 02, 2016 at 02:39:21PM +0100, Jan Kiszka wrote: > On 2016-02-02 14:29, Stefan Hajnoczi wrote: > > Hi Jan, > > In 2011 the following patch was merged to optimize I/O vs vcpu scheduling: > > > > commit c9f711a5d31e22dac932c1c01e9c0f97caff0988 > > Author: Jan Kiszka <jan.kis...@siemens.com> > > Date: Mon Aug 22 17:46:02 2011 +0200 > > > > Poll main loop after I/O events were received > > > > This was back in the days of CONFIG_IOTHREAD. Things have changed > > quite a bit since then. > > > > Do you think the last_io/non-blocking trick is still needed today in TCG? > > The problem back then was the lock-step between io-thread and vcpus > thread: if the iothread polled with the option to block, the vcpus > thread got kicked again because the common lock was released to it. But > if the iothread did not block because of further pending io, it would > have to kick the vcpus thread immediately out of its emulation loop > again. This meant no progress for the vcpus, only sync ping-pong. > > If this changed now (I lost a bit track), the need for this trick might > be gone. Maybe try the setup I described and measure the boot time of an > SMP guest with and without this trick.
Okay, thanks. Stefan
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