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2e9d1e150a
Thanks to all the work that was done by Andy Lutomirski and others,
enter_from_user_mode() and prepare_exit_to_usermode() are now called only with
interrupts disabled. Let's provide them a version of user_enter()/user_exit()
that skips saving and restoring the interrupt flag.
On an AMD-based machine I tested this patch on, with force-enabled
context tracking, the speed-up in system calls was 90 clock cycles or 6%,
measured with the following simple benchmark:
#include <sys/signal.h>
#include <time.h>
#include <unistd.h>
#include <stdio.h>
unsigned long rdtsc()
{
unsigned long result;
asm volatile("rdtsc; shl $32, %%rdx; mov %%eax, %%eax\n"
"or %%rdx, %%rax" : "=a" (result) : : "rdx");
return result;
}
int main()
{
unsigned long tsc1, tsc2;
int pid = getpid();
int i;
tsc1 = rdtsc();
for (i = 0; i < 100000000; i++)
kill(pid, SIGWINCH);
tsc2 = rdtsc();
printf("%ld\n", tsc2 - tsc1);
}
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kvm@vger.kernel.org
Link: http://lkml.kernel.org/r/1466434712-31440-2-git-send-email-pbonzini@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
144 lines
3.5 KiB
C
144 lines
3.5 KiB
C
#ifndef _LINUX_CONTEXT_TRACKING_H
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#define _LINUX_CONTEXT_TRACKING_H
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#include <linux/sched.h>
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#include <linux/vtime.h>
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#include <linux/context_tracking_state.h>
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#include <asm/ptrace.h>
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#ifdef CONFIG_CONTEXT_TRACKING
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extern void context_tracking_cpu_set(int cpu);
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/* Called with interrupts disabled. */
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extern void __context_tracking_enter(enum ctx_state state);
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extern void __context_tracking_exit(enum ctx_state state);
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extern void context_tracking_enter(enum ctx_state state);
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extern void context_tracking_exit(enum ctx_state state);
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extern void context_tracking_user_enter(void);
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extern void context_tracking_user_exit(void);
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static inline void user_enter(void)
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{
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if (context_tracking_is_enabled())
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context_tracking_enter(CONTEXT_USER);
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}
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static inline void user_exit(void)
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{
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if (context_tracking_is_enabled())
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context_tracking_exit(CONTEXT_USER);
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}
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/* Called with interrupts disabled. */
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static inline void user_enter_irqoff(void)
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{
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if (context_tracking_is_enabled())
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__context_tracking_enter(CONTEXT_USER);
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}
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static inline void user_exit_irqoff(void)
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{
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if (context_tracking_is_enabled())
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__context_tracking_exit(CONTEXT_USER);
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}
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static inline enum ctx_state exception_enter(void)
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{
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enum ctx_state prev_ctx;
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if (!context_tracking_is_enabled())
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return 0;
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prev_ctx = this_cpu_read(context_tracking.state);
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if (prev_ctx != CONTEXT_KERNEL)
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context_tracking_exit(prev_ctx);
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return prev_ctx;
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}
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static inline void exception_exit(enum ctx_state prev_ctx)
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{
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if (context_tracking_is_enabled()) {
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if (prev_ctx != CONTEXT_KERNEL)
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context_tracking_enter(prev_ctx);
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}
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}
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/**
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* ct_state() - return the current context tracking state if known
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*
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* Returns the current cpu's context tracking state if context tracking
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* is enabled. If context tracking is disabled, returns
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* CONTEXT_DISABLED. This should be used primarily for debugging.
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*/
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static inline enum ctx_state ct_state(void)
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{
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return context_tracking_is_enabled() ?
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this_cpu_read(context_tracking.state) : CONTEXT_DISABLED;
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}
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#else
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static inline void user_enter(void) { }
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static inline void user_exit(void) { }
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static inline void user_enter_irqoff(void) { }
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static inline void user_exit_irqoff(void) { }
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static inline enum ctx_state exception_enter(void) { return 0; }
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static inline void exception_exit(enum ctx_state prev_ctx) { }
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static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }
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#endif /* !CONFIG_CONTEXT_TRACKING */
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#define CT_WARN_ON(cond) WARN_ON(context_tracking_is_enabled() && (cond))
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#ifdef CONFIG_CONTEXT_TRACKING_FORCE
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extern void context_tracking_init(void);
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#else
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static inline void context_tracking_init(void) { }
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#endif /* CONFIG_CONTEXT_TRACKING_FORCE */
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#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
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static inline void guest_enter(void)
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{
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if (vtime_accounting_cpu_enabled())
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vtime_guest_enter(current);
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else
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current->flags |= PF_VCPU;
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if (context_tracking_is_enabled())
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__context_tracking_enter(CONTEXT_GUEST);
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}
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static inline void guest_exit(void)
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{
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if (context_tracking_is_enabled())
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__context_tracking_exit(CONTEXT_GUEST);
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if (vtime_accounting_cpu_enabled())
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vtime_guest_exit(current);
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else
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current->flags &= ~PF_VCPU;
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}
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#else
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static inline void guest_enter(void)
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{
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/*
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* This is running in ioctl context so its safe
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* to assume that it's the stime pending cputime
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* to flush.
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*/
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vtime_account_system(current);
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current->flags |= PF_VCPU;
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}
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static inline void guest_exit(void)
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{
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/* Flush the guest cputime we spent on the guest */
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vtime_account_system(current);
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current->flags &= ~PF_VCPU;
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}
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#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
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#endif
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