* 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()? > + > + info->start = start; > + info->end = end; > + info->mm = mm; > + info->stride_shift = stride_shift; > + info->freed_tables = freed_tables; > + info->new_tlb_gen = new_tlb_gen; This pattern is really asking for a bit more tabulation: info->start = start; info->end = end; info->mm = mm; info->stride_shift = stride_shift; info->freed_tables = freed_tables; info->new_tlb_gen = new_tlb_gen; > +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? > + if ((end == TLB_FLUSH_ALL) || > + ((end - start) >> stride_shift) > tlb_single_page_flush_ceiling) { > + start = 0UL; Any reason why we cannot use the '0' numeric literal here? > + struct flush_tlb_info *info; > + > + preempt_disable(); > + > + info = get_flush_tlb_info(NULL, start, end, 0, false, 0); > + > + info = this_cpu_ptr(&flush_tlb_info); > + info->start = start; > + info->end = end; > + > + on_each_cpu(do_kernel_range_flush, info, 1); > + > + put_flush_tlb_info(); > + > + preempt_enable(); > } > } > > void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) > { > - struct flush_tlb_info info = { > + static const struct flush_tlb_info info = { > .mm = NULL, > .start = 0UL, > .end = TLB_FLUSH_ALL, Could you please move this now .data global variable just before the function, to make it more apparent what's going on? Thanks, Ingo
