On 26 May 2012 09:25, Stas Sergeev wrote: > 26.05.2012 16:48, Bart Oldeman wrote: >> >> On 26 May 2012 08:05, Stas Sergeev wrote: >>> >>> And I already have the mail like "why dosemu is running fast >>> as root, and is slow running as user". I think this change should >>> be undone. Yes, the non-zero lowmem base is a great work, >>> cheers and regards, but, as long as it is hopelessly slower than >>> vm86, I think the user have to be notified the hardest possible way.
I now realise that the person who sent you the mail must have missed the message: Using CPU emulation because vm.mmap_min_addr > 0. For more information, see /home/bart/.dosemu/boot.log. --- perhaps an icon or menu was used. > I don't know how exactly $_cpu_emu option currently works, > but I think it is inconsistent. It seems to me "off" is currently > used as "auto" to default either to "off" or to "vm86", depending > on an arch and on a zero-base availability. If this understanding > is correct, then I propose to make "off" to depend only on an > arch, and invent "auto", which will also take zero-base availability > into account. Good idea. > On a side note, IIRC the qemu people claim that the jit codegen > can be as fast (or faster) than the vm86. Any ideas why this is > not the case with dosemu? :) It just isn't. And of course it doesn't make sense, a jit always has more overhead than native execution. You have to ask them for benchmarks. When I test myself on a simple tight loop (dec ax; jnz back), I see QEMU (1.0.1) being a factor 20 slower than vm86. However DOSEMU's jit was even slower, something I rectified in the two most recent git commits. DOSEMU is faster however when code writes to data within the same page (a common occurance in DOS, not so common in modern OSes), because of the r/w alias, that QEMU does not have. Anyway, the main question is, is it fast enough? Since most of the more speed-demanding DOS apps use DPMI which can be natively executed, and even with a factor 20 slowdown on a synthetic benchmark, the JIT on a 2 GHz PC is still like a 100 MHz Pentium, quite a powerful machine in DOS days. And if you have an older computer, just use a 32 bit kernel and set mmap_min_addr to 0 and things still work (with a security risk -- unplug the network if you're paranoid). Bart ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Dosemu-devel mailing list Dosemu-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dosemu-devel
