lkml.org 
[lkml]   [2021]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH V4 2/2] riscv: Use use_asid_allocator flush TLB
    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.

    \
     
     \ /
      Last update: 2021-05-30 01:43    [W:9.412 / U:0.176 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site