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Re: [Qemu-devel] [PATCH v8 05/25] tcg: add options for enabling MTTCG
From: |
Pranith Kumar |
Subject: |
Re: [Qemu-devel] [PATCH v8 05/25] tcg: add options for enabling MTTCG |
Date: |
Sun, 29 Jan 2017 15:37:38 -0500 |
User-agent: |
mu4e 0.9.17; emacs 25.1.1 |
Alex Bennée writes:
> From: KONRAD Frederic <address@hidden>
>
> 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 <address@hidden>
> [AJB: move to -accel tcg,thread=multi|single, defaults]
> Signed-off-by: Alex Bennée <address@hidden>
> Reviewed-by: Richard Henderson <address@hidden>
> ---
> 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
> ---
> 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..76b6e04332 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_DEFAULT_MO) && defined(TCG_TARGET_DEFAULT_MO)
> + return (TCG_DEFAULT_MO & ~TCG_TARGET_DEFAULT_MO) == 0;
> +#else
> + return false;
> +#endif
> +}
This still doesn't look right. It is saying that a host like ARM will be able
to run guests that have a stronger memory model, no?
--
Pranith
- [Qemu-devel] [PATCH v8 02/25] mttcg: translate-all: Enable locking debug in a debug build, (continued)
- [Qemu-devel] [PATCH v8 02/25] mttcg: translate-all: Enable locking debug in a debug build, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 04/25] tcg: move TCG_MO/BAR types into own file, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 07/25] tcg: rename tcg_current_cpu to tcg_current_rr_cpu, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 01/25] docs: new design document multi-thread-tcg.txt, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 03/25] mttcg: Add missing tb_lock/unlock() in cpu_exec_step(), Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 05/25] tcg: add options for enabling MTTCG, Alex Bennée, 2017/01/27
- Re: [Qemu-devel] [PATCH v8 05/25] tcg: add options for enabling MTTCG,
Pranith Kumar <=
- [Qemu-devel] [PATCH v8 15/25] cputlb: introduce tlb_flush_* async work., Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 10/25] tcg: enable tb_lock() for SoftMMU, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 11/25] tcg: enable thread-per-vCPU, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 13/25] cputlb: add assert_cpu_is_self checks, Alex Bennée, 2017/01/27
- [Qemu-devel] [PATCH v8 08/25] tcg: drop global lock during TCG code execution, Alex Bennée, 2017/01/27