Sergey Fedorov <serge.f...@gmail.com> writes: > On 18/04/16 17:09, Alex Bennée wrote: >> Sergey Fedorov <sergey.fedo...@linaro.org> writes: >>> From: Sergey Fedorov <serge.f...@gmail.com> >>> >>> 'tb_invalidated_flag' was meant to catch two events: >>> * some TB has been invalidated by tb_phys_invalidate(); >>> * the whole translation buffer has been flushed by tb_flush(). >>> >>> Then it was checked: >>> * in cpu_exec() to ensure that the last executed TB can be safely >>> linked to directly call the next one; >>> * in cpu_exec_nocache() to decide if the original TB should be provided >>> for further possible invalidation along with the temporarily >>> generated TB. >>> >>> It is always safe to patch an invalidated TB since it is not going to be >>> used anyway. >> Wouldn't that have implications for code searching through the linked >> list of jump patched TBs? > > The only implication I can see is that the jump in that already > invalidated TB could just get reset back later on in > tb_phys_invalidate(). We could keep track of invalidated TB's and skip > patching those but it's also some overhead in the main CPU execution > loop wich I'm not sure is worth to be introduced. > > (snip) >>> diff --git a/cpu-exec.c b/cpu-exec.c > (snip) >>> @@ -507,14 +510,12 @@ int cpu_exec(CPUState *cpu) >>> } >>> tb_lock(); >>> tb = tb_find_fast(cpu); >>> - /* Note: we do it here to avoid a gcc bug on Mac OS X when >>> - doing it in tb_find_slow */ >> Is this still true? Would it make more sense to push the patching down >> to the gen_code? > > This comment comes up to the commit: > > commit 1538800276aa7228d74f9d00bf275f54dc9e9b43 > Author: bellard <bellard@c046a42c-6fe2-441c-8c8c-71466251a162> > Date: Mon Dec 19 01:42:32 2005 +0000 > > workaround for gcc bug on PowerPC > > > It was added more than ten years ago. Anyway, now this code is here not > because of the bug: we need to reset 'next_tb' which is a local variable > in cpu_exec(). Personally, I don't think it would be neater to hide it > into gen_code(). Do you have some thoughts on how we could benefit from > doing so? BTW, I had a feeling that it may be useful to reorganize > cpu_exec() a bit, although I don't have a solid idea of how to do this > so far.
I'm mainly eyeing the tb_lock/unlock which would be nice to push further down the call chain if we can, especially if the need to lock tb_find_fast can be removed later on. >> >> I got slightly confused as to what next_tb ends up meaning at what point >> in the run loop. > > Yes, it seems to be a misleading name for this variable. As it was > discussed on IRC, I'd like to break it into two variables, say 'last_tb' > and 'tb_exit_idx', as soon as cpu_tb_exec() returns. Probably this > series could also include such a patch. Yes this would be a worthwhile separate patch. > > Kind regards, > Sergey -- Alex Bennée
