Messages in this thread Patch in this message | | | Date | Wed, 20 Jun 2018 14:32:08 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v10 7/7] x86/tsc: use tsc early |
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On Wed, Jun 20, 2018 at 12:42:40PM +0200, Thomas Gleixner wrote: > On Wed, 20 Jun 2018, Peter Zijlstra wrote:
> > I'm still puzzled by the entire need for tsc_early_enabled and all that. > > Esp. since both branches do the exact same thing: > > > > return cycles_2_ns(rdtsc()); > > Right. But up to the point where the real sched_clock initialization can be > done and the static keys can be flipped, there must be a way to > conditinally use TSC depending on availablility and early initialization.
Ah, so we want to flip keys early, can be done, see below.
> You might argue, that we shouldn't care becasue the jiffies case is just > the worst case fallback anyway. I wouldn't even disagree as those old > machines which have TSC varying with the CPU frequency really should not > matter anymore. Pavel might disagree of course.
You forgot (rightfully) that we even use TSC on those !constant machines, we adjust the cycles_2_ns thing from the cpufreq notifiers.
The only case we should _ever_ use that jiffies callback is when TSC really isn't there. Basically, if we kill notsc, we could make native_sched_clock() := cycles_2_ns(rdtsc()) (for CONFIG_X86_TSC), the end.
No static keys, nothing.
That said; flipping static keys early isn't hard. We should call jump_label_init() early, because we want the entries sorted and the key->entries link set. It will also replace the GENERIC_NOP5_ATOMIC thing, which means we need to also do arch_init_ideal_nop() early, but since that is pure CPUID based that should be doable.
And then something like the below could be used.
--- diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c index e56c95be2808..2dd8c5bdd87b 100644 --- a/arch/x86/kernel/jump_label.c +++ b/arch/x86/kernel/jump_label.c @@ -140,4 +140,38 @@ __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, __jump_label_transform(entry, type, text_poke_early, 1); } +void jump_label_update_early(struct static_key *key, bool enable) +{ + struct jump_entry *entry, *stop = __stop___jump_table; + + /* + * We need the table sorted and key->entries set up. + */ + WARN_ON_ONCE(!static_key_initialized); + + entry = static_key_entries(key); + + /* + * Sanity check for early users, there had beter be a core kernel user. + */ + if (!entry || !entry->code || !core_kernel_text(entry->code)) { + WARN_ON(1); + return; + } + + for ( ; (entry < stop) && (jump_entry_key(entry) == key); entry++) { + enum jump_label_type type = enable ^ jump_entry_branch(entry); + __jump_label_transform(entry, type, text_poke_early, 0); + } + + atomic_set_release(&key->enabled, !!enabled); +} + +#else + +void jump_label_update_early(struct static_key *key, bool enable) +{ + atomic_set(&key->enabled, !!enabled); +} + #endif diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h index b46b541c67c4..cac61beca25f 100644 --- a/include/linux/jump_label.h +++ b/include/linux/jump_label.h @@ -79,6 +79,7 @@ #include <linux/types.h> #include <linux/compiler.h> +#include <linux/bug.h> extern bool static_key_initialized; @@ -110,6 +111,17 @@ struct static_key { }; }; +#define JUMP_TYPE_FALSE 0UL +#define JUMP_TYPE_TRUE 1UL +#define JUMP_TYPE_LINKED 2UL +#define JUMP_TYPE_MASK 3UL + +static inline struct jump_entry *static_key_entries(struct static_key *key) +{ + WARN_ON_ONCE(key->type & JUMP_TYPE_LINKED); + return (struct jump_entry *)(key->type & ~JUMP_TYPE_MASK); +} + #else struct static_key { atomic_t enabled; @@ -119,6 +131,17 @@ struct static_key { #ifdef HAVE_JUMP_LABEL #include <asm/jump_label.h> + +static inline struct static_key *jump_entry_key(struct jump_entry *entry) +{ + return (struct static_key *)((unsigned long)entry->key & ~1UL); +} + +static inline bool jump_entry_branch(struct jump_entry *entry) +{ + return (unsigned long)entry->key & 1UL; +} + #endif #ifndef __ASSEMBLY__ @@ -132,11 +155,6 @@ struct module; #ifdef HAVE_JUMP_LABEL -#define JUMP_TYPE_FALSE 0UL -#define JUMP_TYPE_TRUE 1UL -#define JUMP_TYPE_LINKED 2UL -#define JUMP_TYPE_MASK 3UL - static __always_inline bool static_key_false(struct static_key *key) { return arch_static_branch(key, false); diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 01ebdf1f9f40..9710fa7582aa 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -295,12 +295,6 @@ void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry arch_jump_label_transform(entry, type); } -static inline struct jump_entry *static_key_entries(struct static_key *key) -{ - WARN_ON_ONCE(key->type & JUMP_TYPE_LINKED); - return (struct jump_entry *)(key->type & ~JUMP_TYPE_MASK); -} - static inline bool static_key_type(struct static_key *key) { return key->type & JUMP_TYPE_TRUE; @@ -321,16 +315,6 @@ static inline void static_key_set_linked(struct static_key *key) key->type |= JUMP_TYPE_LINKED; } -static inline struct static_key *jump_entry_key(struct jump_entry *entry) -{ - return (struct static_key *)((unsigned long)entry->key & ~1UL); -} - -static bool jump_entry_branch(struct jump_entry *entry) -{ - return (unsigned long)entry->key & 1UL; -} - /*** * A 'struct static_key' uses a union such that it either points directly * to a table of 'struct jump_entry' or to a linked list of modules which in
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