Pranith Kumar <bobby.pr...@gmail.com> writes:
> Hi Alex,
>
> I just spotted this:
>
> On Mon, Feb 6, 2017 at 10:30 AM, Alex Bennée <alex.ben...@linaro.org> wrote:
>
>> From: KONRAD Frederic <fred.kon...@greensocs.com>
>>
>> We know there will be cases where MTTCG won't work until additional work
>> is done in the front/back ends to support. It will however be useful to
>> be able to turn it on.
>>
>> As a result MTTCG will default to off unless the combination is
>> supported. However the user can turn it on for the sake of testing.
>>
>> Signed-off-by: KONRAD Frederic <fred.kon...@greensocs.com>
>> [AJB: move to -accel tcg,thread=multi|single, defaults]
>> Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
>> Reviewed-by: Richard Henderson <r...@twiddle.net>
>> ---
>> v1:
>> - merge with add mttcg option.
>> - update commit message
>> v2:
>> - machine_init->opts_init
>> v3:
>> - moved from -tcg to -accel tcg,thread=single|multi
>> - fix checkpatch warnings
>> v4:
>> - make mttcg_enabled extern, qemu_tcg_mttcg_enabled() now just macro
>> - qemu_tcg_configure now propagates Error instead of exiting
>> - better error checking of thread=foo
>> - use CONFIG flags for default_mttcg_enabled()
>> - disable mttcg with icount, error if both forced on
>> v7
>> - explicitly disable MTTCG for TCG_OVERSIZED_GUEST
>> - use check_tcg_memory_orders_compatible() instead of CONFIG_MTTCG_HOST
>> - change CONFIG_MTTCG_TARGET to TARGET_SUPPORTS_MTTCG
>> v8
>> - fix missing include tcg.h
>> - change mismatched MOs to a warning instead of error
>> v10
>> - TCG_DEFAULT_MO -> TCG_GUEST_DEFAULT_MO
>> ---
>> cpus.c | 72 ++++++++++++++++++++++++++++++
>> +++++++++++++++++++++
>> include/qom/cpu.h | 9 +++++++
>> include/sysemu/cpus.h | 2 ++
>> qemu-options.hx | 20 ++++++++++++++
>> tcg/tcg.h | 9 +++++++
>> vl.c | 49 ++++++++++++++++++++++++++++++++++-
>> 6 files changed, 160 insertions(+), 1 deletion(-)
>>
>> diff --git a/cpus.c b/cpus.c
>> index 71a82e5004..6a7e5a50d8 100644
>> --- a/cpus.c
>> +++ b/cpus.c
>> @@ -25,6 +25,7 @@
>> /* Needed early for CONFIG_BSD etc. */
>> #include "qemu/osdep.h"
>> #include "qemu-common.h"
>> +#include "qemu/config-file.h"
>> #include "cpu.h"
>> #include "monitor/monitor.h"
>> #include "qapi/qmp/qerror.h"
>> @@ -45,6 +46,7 @@
>> #include "qemu/main-loop.h"
>> #include "qemu/bitmap.h"
>> #include "qemu/seqlock.h"
>> +#include "tcg.h"
>> #include "qapi-event.h"
>> #include "hw/nmi.h"
>> #include "sysemu/replay.h"
>> @@ -150,6 +152,76 @@ typedef struct TimersState {
>> } TimersState;
>>
>> static TimersState timers_state;
>> +bool mttcg_enabled;
>> +
>> +/*
>> + * We default to false if we know other options have been enabled
>> + * which are currently incompatible with MTTCG. Otherwise when each
>> + * guest (target) has been updated to support:
>> + * - atomic instructions
>> + * - memory ordering primitives (barriers)
>> + * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
>> + *
>> + * Once a guest architecture has been converted to the new primitives
>> + * there are two remaining limitations to check.
>> + *
>> + * - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
>> + * - The host must have a stronger memory order than the guest
>> + *
>> + * It may be possible in future to support strong guests on weak hosts
>> + * but that will require tagging all load/stores in a guest with their
>> + * implicit memory order requirements which would likely slow things
>> + * down a lot.
>> + */
>> +
>> +static bool check_tcg_memory_orders_compatible(void)
>> +{
>> +#if defined(TCG_GUEST_DEFAULT_MO) && defined(TCG_TARGET_DEFAULT_MO)
>> + return (TCG_GUEST_DEFAULT_MO & ~TCG_TARGET_DEFAULT_MO) == 0;
>> +#else
>> + return false;
>> +#endif
>> +}
>> +
>> +static bool default_mttcg_enabled(void)
>> +{
>> + QemuOpts *icount_opts = qemu_find_opts_singleton("icount");
>> + const char *rr = qemu_opt_get(icount_opts, "rr");
>> +
>> + if (rr || TCG_OVERSIZED_GUEST) {
>> + return false;
>> + } else {
>> +#ifdef TARGET_SUPPORTS_MTTCG
>> + return check_tcg_memory_orders_compatible();
>> +#else
>> + return false;
>> +#endif
>> + }
>> +}
>> +
>> +void qemu_tcg_configure(QemuOpts *opts, Error **errp)
>> +{
>> + const char *t = qemu_opt_get(opts, "thread");
>> + if (t) {
>> + if (strcmp(t, "multi") == 0) {
>> + if (TCG_OVERSIZED_GUEST) {
>> + error_setg(errp, "No MTTCG when guest word size > hosts");
>> + } else {
>> + if (!check_tcg_memory_orders_compatible()) {
>> + error_report("Guest requires stronger MO that host");
>>
>
> s/MO that host/MO than host/?
Good catch.
>
> Also, this message is a bit cryptic for end users. How about saying "Guest
> and host architectures are incompatible, you may encounter errors!" or
> something similar?
"Guest assumes a stronger memory ordering than the host provides, this
may cause strange/hard to debug errors."
?
>
> Thanks,
--
Alex Bennée
