Messages in this thread |  | | Date | Sat, 29 May 2021 16:42:37 -0700 (PDT) | From | palmerdabbelt@google ... | Subject | Re: [PATCH V4 2/2] riscv: Use use_asid_allocator flush TLB |
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On Thu, 27 May 2021 00:09:03 PDT (-0700), Christoph Hellwig wrote: > On Wed, May 26, 2021 at 05:49:21AM +0000, guoren@kernel.org wrote: >> From: Guo Ren <guoren@linux.alibaba.com> >> >> Use static_branch_unlikely(&use_asid_allocator) to keep the origin >> tlb flush style, so it's no effect on the existing machine. Here >> are the optimized functions: >> - flush_tlb_mm >> - flush_tlb_page >> - flush_tlb_range >> >> All above are based on the below new implement functions: >> - __sbi_tlb_flush_range_asid >> - local_flush_tlb_range_asid >> >> These functions are based on ASID instead of previous non-ASID >> tlb_flush implementation which invalidates more useful tlb >> entries. > > I still think the commit message is incomplete and rather misleading. > Here is what I'd come up with from reading the patch: > > --------- > Subject: add ASID-based tlbflushing methods > > Implement optimized version of the tlb flushing routines for systems > using ASIDs. These are behind the use_asid_allocator static branch to > not affect existing systems not using ASIDs. > ---------
That seems much better, thanks.
>> +static inline void local_flush_tlb_range_asid(unsigned long start, >> + unsigned long size, unsigned long asid) >> +{ >> + unsigned long tmp, end = ALIGN(start + size, PAGE_SIZE); >> + >> + for (tmp = start & PAGE_MASK; tmp < end; tmp += PAGE_SIZE) { >> + __asm__ __volatile__ ("sfence.vma %0, %1" >> + : >> + : "r" (tmp), "r" (asid) >> + : "memory"); >> + tmp += PAGE_SIZE; >> + } > > This double increments tmp. > > Also the non-ASID code switches to a global flush once flushing more > than a single page. It might be worth documenting the tradeoff in the > code.
For some reason I thought we'd written this down in the commentary of teh ISA manual as the suggested huersitic here, but I can't find it so maybe I'm wrong. If it's actually there it would be good to point that out, otherwise some documentation seems fine as it'll probably become a tunable at some point anyway.
>> +static void __sbi_tlb_flush_range_asid(struct cpumask *cmask, >> + unsigned long start, >> + unsigned long size, >> + unsigned long asid) >> +{ > > I don't think the calling conventions here are optimal. I'd pass > the mm_struct as the first argument, as we can derive both the cpumask > and asid from it instead of doing that in the callers. > > But more importantly I think the static branch check can be moved deeper > into the code to avoid a lot of duplication. What do you think of this > version? > > diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h > index b0659413a080..7030837adc1a 100644 > --- a/arch/riscv/include/asm/mmu_context.h > +++ b/arch/riscv/include/asm/mmu_context.h > @@ -33,6 +33,8 @@ static inline int init_new_context(struct task_struct *tsk, > return 0; > } > > +DECLARE_STATIC_KEY_FALSE(use_asid_allocator); > + > #include <asm-generic/mmu_context.h> > > #endif /* _ASM_RISCV_MMU_CONTEXT_H */ > diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c > index 68aa312fc352..45c1b04b105d 100644 > --- a/arch/riscv/mm/context.c > +++ b/arch/riscv/mm/context.c > @@ -18,7 +18,7 @@ > > #ifdef CONFIG_MMU > > -static DEFINE_STATIC_KEY_FALSE(use_asid_allocator); > +DEFINE_STATIC_KEY_FALSE(use_asid_allocator); > > static unsigned long asid_bits; > static unsigned long num_asids; > diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c > index 720b443c4528..d8afbb1269d5 100644 > --- a/arch/riscv/mm/tlbflush.c > +++ b/arch/riscv/mm/tlbflush.c > @@ -4,6 +4,33 @@ > #include <linux/smp.h> > #include <linux/sched.h> > #include <asm/sbi.h> > +#include <asm/mmu_context.h> > + > +static inline void local_flush_tlb_all_asid(unsigned long asid) > +{ > + __asm__ __volatile__ ("sfence.vma x0, %0" > + : > + : "r" (asid) > + : "memory"); > +} > + > +static inline void local_flush_tlb_page_asid(unsigned long addr, > + unsigned long asid) > +{ > + __asm__ __volatile__ ("sfence.vma %0, %1" > + : > + : "r" (addr), "r" (asid) > + : "memory"); > +} > + > +static inline void local_flush_tlb_range_asid(unsigned long start, > + unsigned long size, unsigned long asid) > +{ > + unsigned long addr, end = ALIGN(start + size, PAGE_SIZE); > + > + for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) > + local_flush_tlb_page_asid(addr, asid); > +} > > void flush_tlb_all(void) > { > @@ -12,28 +39,43 @@ void flush_tlb_all(void) > > /* > * This function must not be called with cmask being null. > - * Kernel may panic if cmask is NULL. > */ > -static void __sbi_tlb_flush_range(struct cpumask *cmask, unsigned long start, > +static void __sbi_tlb_flush_range(struct mm_struct *mm, unsigned long start, > unsigned long size) > { > + struct cpumask *cmask = mm_cpumask(mm); > struct cpumask hmask; > unsigned int cpuid; > + bool broadcast; > > if (cpumask_empty(cmask)) > return; > > cpuid = get_cpu(); > + /* check if the tlbflush needs to be sent to other CPUs */ > + broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids; > + if (static_branch_unlikely(&use_asid_allocator)) { > + unsigned long asid = atomic_long_read(&mm->context.id); > > - if (cpumask_any_but(cmask, cpuid) >= nr_cpu_ids) { > - /* local cpu is the only cpu present in cpumask */ > - if (size <= PAGE_SIZE) > + if (broadcast) { > + riscv_cpuid_to_hartid_mask(cmask, &hmask); > + sbi_remote_sfence_vma_asid(cpumask_bits(&hmask), > + start, size, asid); > + } else if (size != -1) { > + local_flush_tlb_range_asid(start, size, asid); > + } else { > + local_flush_tlb_all_asid(asid); > + } > + } else { > + if (broadcast) { > + riscv_cpuid_to_hartid_mask(cmask, &hmask); > + sbi_remote_sfence_vma(cpumask_bits(&hmask), > + start, size); > + } else if (size <= PAGE_SIZE) { > local_flush_tlb_page(start); > - else > + } else { > local_flush_tlb_all(); > - } else { > - riscv_cpuid_to_hartid_mask(cmask, &hmask); > - sbi_remote_sfence_vma(cpumask_bits(&hmask), start, size); > + } > } > > put_cpu(); > @@ -41,16 +83,16 @@ static void __sbi_tlb_flush_range(struct cpumask *cmask, unsigned long start, > > void flush_tlb_mm(struct mm_struct *mm) > { > - __sbi_tlb_flush_range(mm_cpumask(mm), 0, -1); > + __sbi_tlb_flush_range(mm, 0, -1); > } > > void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr) > { > - __sbi_tlb_flush_range(mm_cpumask(vma->vm_mm), addr, PAGE_SIZE); > + __sbi_tlb_flush_range(vma->vm_mm, addr, PAGE_SIZE); > } > > void flush_tlb_range(struct vm_area_struct *vma, unsigned long start, > unsigned long end) > { > - __sbi_tlb_flush_range(mm_cpumask(vma->vm_mm), start, end - start); > + __sbi_tlb_flush_range(vma->vm_mm, start, end - start); > }
LGTM. I took the first one as IMO they're really distnict issues, LMK if you want to re-spin this one or if I should just take what's here.
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