| Message ID | 20210525164541.17985-1-alex.bennee@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [Bug,1896298,RFC] accel/tcg: change default codegen buffer size for i386-softmmu | expand |
Alex Bennée <alex.bennee@linaro.org> writes: > 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. ping?
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.bennee@linaro.org> > Cc: Thomas Huth <thuth@redhat.com> > Cc: 1896298@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. (1) I've got a re-org of this code out for review: https://patchew.org/QEMU/20210502231844.1977630-1-richard.henderson@linaro.org/ (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? r~
Richard Henderson <richard.henderson@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.bennee@linaro.org> >> Cc: Thomas Huth <thuth@redhat.com> >> Cc: 1896298@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.henderson@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~
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 \
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.bennee@linaro.org> Cc: Thomas Huth <thuth@redhat.com> Cc: 1896298@bugs.launchpad.net --- accel/tcg/translate-all.c | 4 ++++ 1 file changed, 4 insertions(+)