* Nadav Amit <[email protected]> wrote:
> > On Apr 25, 2019, at 12:29 PM, Ingo Molnar <[email protected]> wrote: > > > > > > * Nadav Amit <[email protected]> wrote: > > > >> Move flush_tlb_info variables off the stack. This allows to align > >> flush_tlb_info to cache-line and avoid potentially unnecessary cache > >> line movements. It also allows to have a fixed virtual-to-physical > >> translation of the variables, which reduces TLB misses. > >> > >> Use per-CPU struct for flush_tlb_mm_range() and > >> flush_tlb_kernel_range(). Add debug assertions to ensure there are > >> no nested TLB flushes that might overwrite the per-CPU data. For > >> arch_tlbbatch_flush() use a const struct. > >> > >> Results when running a microbenchmarks that performs 10^6 MADV_DONTEED > >> operations and touching a page, in which 3 additional threads run a > >> busy-wait loop (5 runs, PTI and retpolines are turned off): > >> > >> base off-stack > >> ---- --------- > >> avg (usec/op) 1.629 1.570 (-3%) > >> stddev 0.014 0.009 > >> > >> Cc: Peter Zijlstra <[email protected]> > >> Cc: Andy Lutomirski <[email protected]> > >> Cc: Dave Hansen <[email protected]> > >> Cc: Borislav Petkov <[email protected]> > >> Cc: Thomas Gleixner <[email protected]> > >> Signed-off-by: Nadav Amit <[email protected]> > >> > >> --- > >> > >> v1->v2: > >> - Initialize all flush_tlb_info fields [Andy] > >> --- > >> arch/x86/mm/tlb.c | 100 ++++++++++++++++++++++++++++++++++------------ > >> 1 file changed, 74 insertions(+), 26 deletions(-) > >> > >> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c > >> index 487b8474c01c..aac191eb2b90 100644 > >> --- a/arch/x86/mm/tlb.c > >> +++ b/arch/x86/mm/tlb.c > >> @@ -634,7 +634,7 @@ static void flush_tlb_func_common(const struct > >> flush_tlb_info *f, > >> this_cpu_write(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen, mm_tlb_gen); > >> } > >> > >> -static void flush_tlb_func_local(void *info, enum tlb_flush_reason reason) > >> +static void flush_tlb_func_local(const void *info, enum tlb_flush_reason > >> reason) > >> { > >> const struct flush_tlb_info *f = info; > >> > >> @@ -722,43 +722,81 @@ void native_flush_tlb_others(const struct cpumask > >> *cpumask, > >> */ > >> unsigned long tlb_single_page_flush_ceiling __read_mostly = 33; > >> > >> +static DEFINE_PER_CPU_SHARED_ALIGNED(struct flush_tlb_info, > >> flush_tlb_info); > >> + > >> +#ifdef CONFIG_DEBUG_VM > >> +static DEFINE_PER_CPU(unsigned int, flush_tlb_info_idx); > >> +#endif > >> + > >> +static inline struct flush_tlb_info *get_flush_tlb_info(struct mm_struct > >> *mm, > >> + unsigned long start, unsigned long end, > >> + unsigned int stride_shift, bool freed_tables, > >> + u64 new_tlb_gen) > >> +{ > >> + struct flush_tlb_info *info = this_cpu_ptr(&flush_tlb_info); > >> + > >> +#ifdef CONFIG_DEBUG_VM > >> + /* > >> + * Ensure that the following code is non-reentrant and flush_tlb_info > >> + * is not overwritten. This means no TLB flushing is initiated by > >> + * interrupt handlers and machine-check exception handlers. > >> + */ > >> + BUG_ON(this_cpu_inc_return(flush_tlb_info_idx) != 1); > >> +#endif > > > > isn't this effectively VM_BUG_ON()? > > Not exactly. When CONFIG_DEBUG_VM is off we get > > #define VM_BUG_ON(cond) BUILD_BUG_ON_INVALID(cond) > > This will cause the build to fail since flush_tlb_info_idx is not defined in > when CONFIG_DEBUG_VM is off. Ugh, so VM_BUG_ON() should really be named VM_BUILD_BUG_ON()? Anyway, agreed. > >> +static inline void put_flush_tlb_info(void) > >> +{ > >> +#ifdef CONFIG_DEBUG_VM > >> + /* Complete reentrency prevention checks */ > >> + barrier(); > >> + this_cpu_dec(flush_tlb_info_idx); > >> +#endif > > > > In principle this_cpu_dec() should imply a compiler barrier? > > this_cpu_dec() is eventually expanded to the macro of percpu_add_op(). And > the inline assembly does not have a “memory” clobber, so I don’t think so. I think that's a bug and PeterZ is fixing those. Thanks, Ingo
