On 2011-02-08 11:06, Aurelien Jarno wrote: > Jan Kiszka a écrit : >> 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. > > Yes, it's slow. But is it a problem? You assume that people use QEMU > only for emulating SMP platforms. This is a wrong assumption. Beside the > x86 target, only sparc really supports SMP emulation.
That's too nearsighted. SMP will be commodity on practically _any_ arch within the next years. And if QEMU doesn't keep up with it, feature and performance-wise, it will loose market share. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
