On 2011-02-08 10:58, Aurelien Jarno wrote: > Jan Kiszka a écrit : >> On 2011-02-08 10:05, Aurelien Jarno wrote: >>> Jan Kiszka a écrit : >>>> On 2011-02-08 09:08, Paolo Bonzini wrote: >>>>> On 02/08/2011 08:26 AM, Aurelien Jarno wrote: >>>>>> I forget to remember when we decided that AIO should be implemented on >>>>>> any host OS. Any pointer? >>>>> To be fair, I/O-heavy workloads are almost unusable without AIO. For >>>>> Window targets, they also crash under SMP due to the Windows AP >>>>> watchdog. But then TCG and SMP do not go very well together anyway. >>>>> >>>>> However, I think deprecating Win32 support would be a very bad idea. >>>> It would be too early at this point. >>>> >>>> But if Windows is once the only reason to keep tons of hardly tested >>>> code paths around or to invest significant additional effort to change >>>> logic or interfaces in this area, than I would prefer that step. I'm >>>> hacking on IOTHREAD vs. !IOTHREAD for some weeks now, and all those >>>> subtle differences are really a PITA and source of various breakages. >>>> >>>> People interested in that platform should finally realize that its fate >>>> is coupled to reducing the #ifdefs as well as the design differences we >>>> see right now and even more in the future. >>>> >>> The guilty here is IOTHREAD. Windows support predates IOTHREAD concept, >>> it's just that people who introduce IOTHREAD didn't care about Windows >>> support at all and added these #ifdef. Disabling Windows support because >>> of that is not fair. >> >> The TCG execution model won't scale long-term. It's already a main to >> boot a quad or just dual core VM, even more when your host has at least >> as many real cores. I'm sure we'll see multi-threaded TCG CPUs in the >> future, and the iothread will just be one of 7, 17 or 257 threads. >> > > And what's the issue with that? People don't always look for performance > when using QEMU. They even often try to emulate old machines (and non > x86 ones), which anyway only have one CPU. This won't change in 5 years, > the only thing is that those machines will be 5 years older. > > People have to keep in mind that QEMU doesn't mean only virtualization > and doesn't mean only x86.
I'm not talking about virtualization here. I'm talking about usable emulation of today's (!) embedded multi-core platforms. It matters a lot if your test roundtrip for booting into a SMP guest and running some apps is a few 10 seconds, a few minutes or even not practically working. Ever tried to boot a 16 core VM in emulation mode? I did, for fun. I just hope I'll never depend on this for work. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
