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author | Ingo Molnar <mingo@kernel.org> | 2015-03-16 15:49:30 +0100 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2015-03-16 15:49:30 +0100 |
commit | 1524b745406a85ba201cb25df72110c1ccac0f72 (patch) | |
tree | 66e4ac8b03dab66849ef815d836a25f38da61a91 /include/linux | |
parent | fba9e07208c0f9d92d9f73761c99c8612039da44 (diff) | |
parent | 126a6a542446f1a49b9f3c69237c87df3eb4e6e1 (diff) |
Merge branch 'nohz/guest' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/nohz
Pull full dynticks support for virt guests from Frederic Weisbecker:
"Some measurements showed that disabling the tick on the host while the
guest is running can be interesting on some workloads. Indeed the
host tick is irrelevant while a vcpu runs, it consumes CPU time and cache
footprint for no good reasons.
Full dynticks already works in every context, but RCU prevents it to
be effective outside userspace, because the CPU needs to take part of
RCU grace period completion as long as RCU may be used on it, which is
the case in kernel context.
However guest is similar to userspace and idle in that we know RCU is
unused on such context. Therefore a CPU in guest/userspace/idle context
can let other CPUs report its own RCU quiescent state on its behalf
and shut down the tick safely, provided it isn't needed for other
reasons than RCU. This is called RCU extended quiescent state.
This was already implemented for idle and userspace. This patchset now
brings it for guest contexts through the following steps:
- Generalize the context tracking APIs to also track guest state
- Rename/sanitize a few CPP symbols accordingly
- Report guest entry/exit to RCU and define this context area as an RCU
extended quiescent state."
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux')
-rw-r--r-- | include/linux/context_tracking.h | 15 | ||||
-rw-r--r-- | include/linux/context_tracking_state.h | 9 | ||||
-rw-r--r-- | include/linux/kvm_host.h | 3 |
3 files changed, 20 insertions, 7 deletions
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index 37b81bd51ec0..2821838256b4 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -10,6 +10,8 @@ #ifdef CONFIG_CONTEXT_TRACKING extern void context_tracking_cpu_set(int cpu); +extern void context_tracking_enter(enum ctx_state state); +extern void context_tracking_exit(enum ctx_state state); extern void context_tracking_user_enter(void); extern void context_tracking_user_exit(void); extern void __context_tracking_task_switch(struct task_struct *prev, @@ -35,7 +37,8 @@ static inline enum ctx_state exception_enter(void) return 0; prev_ctx = this_cpu_read(context_tracking.state); - context_tracking_user_exit(); + if (prev_ctx != CONTEXT_KERNEL) + context_tracking_exit(prev_ctx); return prev_ctx; } @@ -43,8 +46,8 @@ static inline enum ctx_state exception_enter(void) static inline void exception_exit(enum ctx_state prev_ctx) { if (context_tracking_is_enabled()) { - if (prev_ctx == IN_USER) - context_tracking_user_enter(); + if (prev_ctx != CONTEXT_KERNEL) + context_tracking_enter(prev_ctx); } } @@ -78,10 +81,16 @@ static inline void guest_enter(void) vtime_guest_enter(current); else current->flags |= PF_VCPU; + + if (context_tracking_is_enabled()) + context_tracking_enter(CONTEXT_GUEST); } static inline void guest_exit(void) { + if (context_tracking_is_enabled()) + context_tracking_exit(CONTEXT_GUEST); + if (vtime_accounting_enabled()) vtime_guest_exit(current); else diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h index 97a81225d037..6b7b96a32b75 100644 --- a/include/linux/context_tracking_state.h +++ b/include/linux/context_tracking_state.h @@ -13,8 +13,9 @@ struct context_tracking { */ bool active; enum ctx_state { - IN_KERNEL = 0, - IN_USER, + CONTEXT_KERNEL = 0, + CONTEXT_USER, + CONTEXT_GUEST, } state; }; @@ -34,11 +35,13 @@ static inline bool context_tracking_cpu_is_enabled(void) static inline bool context_tracking_in_user(void) { - return __this_cpu_read(context_tracking.state) == IN_USER; + return __this_cpu_read(context_tracking.state) == CONTEXT_USER; } #else static inline bool context_tracking_in_user(void) { return false; } static inline bool context_tracking_active(void) { return false; } +static inline bool context_tracking_is_enabled(void) { return false; } +static inline bool context_tracking_cpu_is_enabled(void) { return false; } #endif /* CONFIG_CONTEXT_TRACKING */ #endif diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index d12b2104d19b..cc8c61c5459c 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -766,7 +766,8 @@ static inline void kvm_guest_enter(void) * one time slice). Lets treat guest mode as quiescent state, just like * we do with user-mode execution. */ - rcu_virt_note_context_switch(smp_processor_id()); + if (!context_tracking_cpu_is_enabled()) + rcu_virt_note_context_switch(smp_processor_id()); } static inline void kvm_guest_exit(void) |