Richard Henderson <richard.hender...@linaro.org> writes:
> On 5/25/21 9:45 AM, Alex Bennée wrote: >> There are two justifications for making this change. The first is that >> i386 emulation is typically for smaller machines where having a 1gb of >> generated code is overkill for basic emulation. The second is the >> propensity of self-modifying code (c.f. Doom/edit) utilised on i386 >> systems can trigger a rapid growth in invalidated and re-translated >> buffers. This is seen in bug #283. Execution is still inefficient but >> at least the host memory isn't so aggressively used up. >> That said it's still really just a sticking plaster for user >> convenience. >> Signed-off-by: Alex Bennée <alex.ben...@linaro.org> >> Cc: Thomas Huth <th...@redhat.com> >> Cc: 1896...@bugs.launchpad.net >> --- >> accel/tcg/translate-all.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c >> index 640ff6e3e7..f442165674 100644 >> --- a/accel/tcg/translate-all.c >> +++ b/accel/tcg/translate-all.c >> @@ -951,9 +951,13 @@ static void page_lock_pair(PageDesc **ret_p1, >> tb_page_addr_t phys1, >> * Users running large scale system emulation may want to tweak their >> * runtime setup via the tb-size control on the command line. >> */ >> +#ifdef TARGET_I386 >> +#define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB) >> +#else >> #define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (1 * GiB) >> #endif >> #endif >> +#endif >> #define DEFAULT_CODE_GEN_BUFFER_SIZE \ >> (DEFAULT_CODE_GEN_BUFFER_SIZE_1 < MAX_CODE_GEN_BUFFER_SIZE \ >> > > I'm not thrilled, as it is ultra-hacky. I don't disagree. > (1) I've got a re-org of this code out for review: > https://patchew.org/QEMU/20210502231844.1977630-1-richard.hender...@linaro.org/ OK I'll have a look at that. > (2) I'm keen to reorg TCG such that it gets compiled once. There's > currently nothing standing in the way of that except work. But this > would introduce a use of a target-specific define for the first time > into tcg/. I guess I could leave the default sizing back in > accel/tcg/ and pass in the default. > > Other options? Some random thoughts in no particular order: - a separately flushable translation region for code we detect as SMC heavy - a front-end interpreter for SMC code - smarter code generation that dynamically loads values from codemem (usually the SMC code is just tweaking an #imm value) None of these seem particularly amenable to a clean non-complex implementation though. A front-end interpreter would be useful for other things though - it could even be incomplete and handle only common code patterns falling back to full generation for anything it can't handle. > > > r~ -- Alex Bennée
