On Mon, Jul 10, 2017 at 14:05:01 +0200, Paolo Bonzini wrote: > On 09/07/2017 09:50, Emilio G. Cota wrote: > > User-mode is kept out of this: contention due to concurrent translation > > is more commonly found in full-system mode. > > Out of curiosity, is it harder or you just didn't try? It would be nice > if the commit message mentioned the problems (if any) in addition to the > reason why you didn't do it. > > Having similar policies for user and softmmu emulation is much more > maintainable (for an earlier example, see the unification of user mode > emulation's start/end_exclusive logic with softmmu's "safe work").
I agree that it would be nice to have the same mechanism for all. The main hurdle I see is how to allow for concurrent code generation while minimizing flushes of the single, fixed-size[*] code_gen_buffer. In user-mode this is tricky because there is no way to bound the number of threads that might be spawned by the guest code (I don't think reading /proc/sys/kernel/threads-max is a viable solution here). Switching to a "__thread *tcg_ctx_ptr" model will help minimize user-mode/softmmu differences though. The only remaining difference would be that user-mode would need tb_lock() around tb_gen_code, whereas softmmu wouldn't, but everything else would be the same. E. [*] Note that in user-mode we use code_gen_buffer defined at compile-time as a static buffer[].