mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-18 11:57:03 +07:00
8f898fbbe5
Dick Fowles, Don Zickus and Joe Mario have been working on improvements to perf, and noticed heavy cache line contention on the mm_cpumask, running linpack on a 60 core / 120 thread system. The cause turned out to be unnecessary atomic accesses to the mm_cpumask. When in lazy TLB mode, the CPU is only removed from the mm_cpumask if there is a TLB flush event. Most of the time, no such TLB flush happens, and the kernel skips the TLB reload. It can also skip the atomic memory set & test. Here is a summary of Joe's test results: * The __schedule function dropped from 24% of all program cycles down to 5.5%. * The cacheline contention/hotness for accesses to that bitmask went from being the 1st/2nd hottest - down to the 84th hottest (0.3% of all shared misses which is now quite cold) * The average load latency for the bit-test-n-set instruction in __schedule dropped from 10k-15k cycles down to an average of 600 cycles. * The linpack program results improved from 133 GFlops to 144 GFlops. Peak GFlops rose from 133 to 153. Reported-by: Don Zickus <dzickus@redhat.com> Reported-by: Joe Mario <jmario@redhat.com> Tested-by: Joe Mario <jmario@redhat.com> Signed-off-by: Rik van Riel <riel@redhat.com> Reviewed-by: Paul Turner <pjt@google.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/20130731221421.616d3d20@annuminas.surriel.com [ Made the comments consistent around the modified code. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
100 lines
2.4 KiB
C
100 lines
2.4 KiB
C
#ifndef _ASM_X86_MMU_CONTEXT_H
|
|
#define _ASM_X86_MMU_CONTEXT_H
|
|
|
|
#include <asm/desc.h>
|
|
#include <linux/atomic.h>
|
|
#include <asm/pgalloc.h>
|
|
#include <asm/tlbflush.h>
|
|
#include <asm/paravirt.h>
|
|
#ifndef CONFIG_PARAVIRT
|
|
#include <asm-generic/mm_hooks.h>
|
|
|
|
static inline void paravirt_activate_mm(struct mm_struct *prev,
|
|
struct mm_struct *next)
|
|
{
|
|
}
|
|
#endif /* !CONFIG_PARAVIRT */
|
|
|
|
/*
|
|
* Used for LDT copy/destruction.
|
|
*/
|
|
int init_new_context(struct task_struct *tsk, struct mm_struct *mm);
|
|
void destroy_context(struct mm_struct *mm);
|
|
|
|
|
|
static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
|
|
{
|
|
#ifdef CONFIG_SMP
|
|
if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK)
|
|
this_cpu_write(cpu_tlbstate.state, TLBSTATE_LAZY);
|
|
#endif
|
|
}
|
|
|
|
static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
|
|
struct task_struct *tsk)
|
|
{
|
|
unsigned cpu = smp_processor_id();
|
|
|
|
if (likely(prev != next)) {
|
|
#ifdef CONFIG_SMP
|
|
this_cpu_write(cpu_tlbstate.state, TLBSTATE_OK);
|
|
this_cpu_write(cpu_tlbstate.active_mm, next);
|
|
#endif
|
|
cpumask_set_cpu(cpu, mm_cpumask(next));
|
|
|
|
/* Re-load page tables */
|
|
load_cr3(next->pgd);
|
|
|
|
/* Stop flush ipis for the previous mm */
|
|
cpumask_clear_cpu(cpu, mm_cpumask(prev));
|
|
|
|
/* Load the LDT, if the LDT is different: */
|
|
if (unlikely(prev->context.ldt != next->context.ldt))
|
|
load_LDT_nolock(&next->context);
|
|
}
|
|
#ifdef CONFIG_SMP
|
|
else {
|
|
this_cpu_write(cpu_tlbstate.state, TLBSTATE_OK);
|
|
BUG_ON(this_cpu_read(cpu_tlbstate.active_mm) != next);
|
|
|
|
if (!cpumask_test_cpu(cpu, mm_cpumask(next))) {
|
|
/*
|
|
* On established mms, the mm_cpumask is only changed
|
|
* from irq context, from ptep_clear_flush() while in
|
|
* lazy tlb mode, and here. Irqs are blocked during
|
|
* schedule, protecting us from simultaneous changes.
|
|
*/
|
|
cpumask_set_cpu(cpu, mm_cpumask(next));
|
|
/*
|
|
* We were in lazy tlb mode and leave_mm disabled
|
|
* tlb flush IPI delivery. We must reload CR3
|
|
* to make sure to use no freed page tables.
|
|
*/
|
|
load_cr3(next->pgd);
|
|
load_LDT_nolock(&next->context);
|
|
}
|
|
}
|
|
#endif
|
|
}
|
|
|
|
#define activate_mm(prev, next) \
|
|
do { \
|
|
paravirt_activate_mm((prev), (next)); \
|
|
switch_mm((prev), (next), NULL); \
|
|
} while (0);
|
|
|
|
#ifdef CONFIG_X86_32
|
|
#define deactivate_mm(tsk, mm) \
|
|
do { \
|
|
lazy_load_gs(0); \
|
|
} while (0)
|
|
#else
|
|
#define deactivate_mm(tsk, mm) \
|
|
do { \
|
|
load_gs_index(0); \
|
|
loadsegment(fs, 0); \
|
|
} while (0)
|
|
#endif
|
|
|
|
#endif /* _ASM_X86_MMU_CONTEXT_H */
|