Re: [PATCH 1/1] powerpc: kvm: Reduce calls to get current->mm by storing the value locally

Leonardo Bras
2019-09-24T01:22:30Z

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I have done a very simple comparison with gdb disassemble:
By applying this patch, there was a reduction in the function size from
882 to 878 instructions.

(It's a resend, due to not having all the correct lists on my previous
mail)

On Mon, 2019-09-23 at 18:30 -0300, Leonardo Bras wrote:
> Reduces the number of calls to get_current() in order to get the value of
> current->mm by doing it once and storing the value, since it is not
> supposed to change inside the same process).
>
> Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
> ---
> Re-sending to all lists involved. (I missed kvm ones)
>
> arch/powerpc/kvm/book3s_64_mmu_hv.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 9a75f0e1933b..f2b9aea43216 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -508,6 +508,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
> struct vm_area_struct *vma;
> unsigned long rcbits;
> long mmio_update;
> + struct mm_struct *mm;
>
> if (kvm_is_radix(kvm))
> return kvmppc_book3s_radix_page_fault(run, vcpu, ea, dsisr);
> @@ -584,6 +585,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
> is_ci = false;
> pfn = 0;
> page = NULL;
> + mm = current->mm;
> pte_size = PAGE_SIZE;
> writing = (dsisr & DSISR_ISSTORE) != 0;
> /* If writing != 0, then the HPTE must allow writing, if we get here */
> @@ -592,8 +594,8 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
> npages = get_user_pages_fast(hva, 1, writing ? FOLL_WRITE : 0, pages);
> if (npages < 1) {
> /* Check if it's an I/O mapping */
> - down_read(&current->mm->mmap_sem);
> - vma = find_vma(current->mm, hva);
> + down_read(&mm->mmap_sem);
> + vma = find_vma(mm, hva);
> if (vma && vma->vm_start <= hva && hva + psize <= vma->vm_end &&
> (vma->vm_flags & VM_PFNMAP)) {
> pfn = vma->vm_pgoff +
> @@ -602,7 +604,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
> is_ci = pte_ci(__pte((pgprot_val(vma->vm_page_prot))));
> write_ok = vma->vm_flags & VM_WRITE;
> }
> - up_read(&current->mm->mmap_sem);
> + up_read(&mm->mmap_sem);
> if (!pfn)
> goto out_put;
> } else {
> @@ -621,8 +623,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
> * hugepage split and collapse.
> */
> local_irq_save(flags);
> - ptep = find_current_mm_pte(current->mm->pgd,
> - hva, NULL, NULL);
> + ptep = find_current_mm_pte(mm->pgd, hva, NULL, NULL);
> if (ptep) {
> pte = kvmppc_read_update_linux_pte(ptep, 1);
> if (__pte_write(pte))

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