| Message ID | 20210125141044.380156-3-wangyanan55@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Performance improvement about cache flush | expand |
On Mon, Jan 25, 2021 at 10:10:44PM +0800, Yanan Wang wrote: > After dirty-logging is stopped for a VM configured with huge mappings, > KVM will recover the table mappings back to block mappings. As we only > replace the existing page tables with a block entry and the cacheability > has not been changed, the cache maintenance opreations can be skipped. > > Signed-off-by: Yanan Wang <wangyanan55@huawei.com> > --- > arch/arm64/kvm/mmu.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 8e8549ea1d70..37b427dcbc4f 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -744,7 +744,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > { > int ret = 0; > bool write_fault, writable, force_pte = false; > - bool exec_fault; > + bool exec_fault, adjust_hugepage; > bool device = false; > unsigned long mmu_seq; > struct kvm *kvm = vcpu->kvm; > @@ -872,12 +872,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > mark_page_dirty(kvm, gfn); > } > > - if (fault_status != FSC_PERM && !device) > + /* > + * There is no necessity to perform cache maintenance operations if we > + * will only replace the existing table mappings with a block mapping. > + */ > + adjust_hugepage = fault_granule < vma_pagesize ? true : false; nit: you don't need the '? true : false' part That said, your previous patch checks for 'fault_granule > vma_pagesize', so I'm not sure the local variable helps all that much here because it obscures the size checks in my opinion. It would be more straight-forward if we could structure the logic as: if (fault_granule < vma_pagesize) { } else if (fault_granule > vma_page_size) { } else { } With some comments describing what we can infer about the memcache and cache maintenance requirements for each case. Will
On 2021/3/9 0:34, Will Deacon wrote: > On Mon, Jan 25, 2021 at 10:10:44PM +0800, Yanan Wang wrote: >> After dirty-logging is stopped for a VM configured with huge mappings, >> KVM will recover the table mappings back to block mappings. As we only >> replace the existing page tables with a block entry and the cacheability >> has not been changed, the cache maintenance opreations can be skipped. >> >> Signed-off-by: Yanan Wang <wangyanan55@huawei.com> >> --- >> arch/arm64/kvm/mmu.c | 12 +++++++++--- >> 1 file changed, 9 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >> index 8e8549ea1d70..37b427dcbc4f 100644 >> --- a/arch/arm64/kvm/mmu.c >> +++ b/arch/arm64/kvm/mmu.c >> @@ -744,7 +744,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >> { >> int ret = 0; >> bool write_fault, writable, force_pte = false; >> - bool exec_fault; >> + bool exec_fault, adjust_hugepage; >> bool device = false; >> unsigned long mmu_seq; >> struct kvm *kvm = vcpu->kvm; >> @@ -872,12 +872,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >> mark_page_dirty(kvm, gfn); >> } >> >> - if (fault_status != FSC_PERM && !device) >> + /* >> + * There is no necessity to perform cache maintenance operations if we >> + * will only replace the existing table mappings with a block mapping. >> + */ >> + adjust_hugepage = fault_granule < vma_pagesize ? true : false; > nit: you don't need the '? true : false' part > > That said, your previous patch checks for 'fault_granule > vma_pagesize', > so I'm not sure the local variable helps all that much here because it > obscures the size checks in my opinion. It would be more straight-forward > if we could structure the logic as: > > > if (fault_granule < vma_pagesize) { > > } else if (fault_granule > vma_page_size) { > > } else { > > } > > With some comments describing what we can infer about the memcache and cache > maintenance requirements for each case. Thanks for your suggestion here, Will. But I have resent another newer series [1] (KVM: arm64: Improve efficiency of stage2 page table) recently, which has the same theme but different solutions that I think are better. [1] https://lore.kernel.org/lkml/20210208112250.163568-1-wangyanan55@huawei.com/ Could you please comment on that series ? I think it can be found in your inbox :). Thanks, Yanan > > Will > .
On Tue, 09 Mar 2021 08:34:43 +0000, "wangyanan (Y)" <wangyanan55@huawei.com> wrote: > > > On 2021/3/9 0:34, Will Deacon wrote: > > On Mon, Jan 25, 2021 at 10:10:44PM +0800, Yanan Wang wrote: > >> After dirty-logging is stopped for a VM configured with huge mappings, > >> KVM will recover the table mappings back to block mappings. As we only > >> replace the existing page tables with a block entry and the cacheability > >> has not been changed, the cache maintenance opreations can be skipped. > >> > >> Signed-off-by: Yanan Wang <wangyanan55@huawei.com> > >> --- > >> arch/arm64/kvm/mmu.c | 12 +++++++++--- > >> 1 file changed, 9 insertions(+), 3 deletions(-) > >> > >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > >> index 8e8549ea1d70..37b427dcbc4f 100644 > >> --- a/arch/arm64/kvm/mmu.c > >> +++ b/arch/arm64/kvm/mmu.c > >> @@ -744,7 +744,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > >> { > >> int ret = 0; > >> bool write_fault, writable, force_pte = false; > >> - bool exec_fault; > >> + bool exec_fault, adjust_hugepage; > >> bool device = false; > >> unsigned long mmu_seq; > >> struct kvm *kvm = vcpu->kvm; > >> @@ -872,12 +872,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > >> mark_page_dirty(kvm, gfn); > >> } > >> - if (fault_status != FSC_PERM && !device) > >> + /* > >> + * There is no necessity to perform cache maintenance operations if we > >> + * will only replace the existing table mappings with a block mapping. > >> + */ > >> + adjust_hugepage = fault_granule < vma_pagesize ? true : false; > > nit: you don't need the '? true : false' part > > > > That said, your previous patch checks for 'fault_granule > vma_pagesize', > > so I'm not sure the local variable helps all that much here because it > > obscures the size checks in my opinion. It would be more straight-forward > > if we could structure the logic as: > > > > > > if (fault_granule < vma_pagesize) { > > > > } else if (fault_granule > vma_page_size) { > > > > } else { > > > > } > > > > With some comments describing what we can infer about the memcache and cache > > maintenance requirements for each case. > Thanks for your suggestion here, Will. > But I have resent another newer series [1] (KVM: arm64: Improve > efficiency of stage2 page table) > recently, which has the same theme but different solutions that I > think are better. > [1] > https://lore.kernel.org/lkml/20210208112250.163568-1-wangyanan55@huawei.com/ > > Could you please comment on that series ? I think it can be found in > your inbox :). There were already a bunch of comments on that series, and I stopped at the point where the cache maintenance was broken. Please respin that series if you want further feedback on it. In the future, if you deprecate a series (which is completely understandable), please leave a note on the list with a pointer to the new series so that people don't waste time reviewing an obsolete series. Or post the new series with a new version number so that it is obvious that the original series has been superseded. Thanks, M.
On 2021/3/9 16:43, Marc Zyngier wrote: > On Tue, 09 Mar 2021 08:34:43 +0000, > "wangyanan (Y)" <wangyanan55@huawei.com> wrote: >> >> On 2021/3/9 0:34, Will Deacon wrote: >>> On Mon, Jan 25, 2021 at 10:10:44PM +0800, Yanan Wang wrote: >>>> After dirty-logging is stopped for a VM configured with huge mappings, >>>> KVM will recover the table mappings back to block mappings. As we only >>>> replace the existing page tables with a block entry and the cacheability >>>> has not been changed, the cache maintenance opreations can be skipped. >>>> >>>> Signed-off-by: Yanan Wang <wangyanan55@huawei.com> >>>> --- >>>> arch/arm64/kvm/mmu.c | 12 +++++++++--- >>>> 1 file changed, 9 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >>>> index 8e8549ea1d70..37b427dcbc4f 100644 >>>> --- a/arch/arm64/kvm/mmu.c >>>> +++ b/arch/arm64/kvm/mmu.c >>>> @@ -744,7 +744,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>>> { >>>> int ret = 0; >>>> bool write_fault, writable, force_pte = false; >>>> - bool exec_fault; >>>> + bool exec_fault, adjust_hugepage; >>>> bool device = false; >>>> unsigned long mmu_seq; >>>> struct kvm *kvm = vcpu->kvm; >>>> @@ -872,12 +872,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>>> mark_page_dirty(kvm, gfn); >>>> } >>>> - if (fault_status != FSC_PERM && !device) >>>> + /* >>>> + * There is no necessity to perform cache maintenance operations if we >>>> + * will only replace the existing table mappings with a block mapping. >>>> + */ >>>> + adjust_hugepage = fault_granule < vma_pagesize ? true : false; >>> nit: you don't need the '? true : false' part >>> >>> That said, your previous patch checks for 'fault_granule > vma_pagesize', >>> so I'm not sure the local variable helps all that much here because it >>> obscures the size checks in my opinion. It would be more straight-forward >>> if we could structure the logic as: >>> >>> >>> if (fault_granule < vma_pagesize) { >>> >>> } else if (fault_granule > vma_page_size) { >>> >>> } else { >>> >>> } >>> >>> With some comments describing what we can infer about the memcache and cache >>> maintenance requirements for each case. >> Thanks for your suggestion here, Will. >> But I have resent another newer series [1] (KVM: arm64: Improve >> efficiency of stage2 page table) >> recently, which has the same theme but different solutions that I >> think are better. >> [1] >> https://lore.kernel.org/lkml/20210208112250.163568-1-wangyanan55@huawei.com/ >> >> Could you please comment on that series ? I think it can be found in >> your inbox :). > There were already a bunch of comments on that series, and I stopped > at the point where the cache maintenance was broken. Please respin > that series if you want further feedback on it. Ok, I will send a new version later. > > In the future, if you deprecate a series (which is completely > understandable), please leave a note on the list with a pointer to the > new series so that people don't waste time reviewing an obsolete > series. Or post the new series with a new version number so that it is > obvious that the original series has been superseded. I apologize for this, I will be more careful in the future. Thanks, Yanan > Thanks, > > M. >
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 8e8549ea1d70..37b427dcbc4f 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -744,7 +744,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, { int ret = 0; bool write_fault, writable, force_pte = false; - bool exec_fault; + bool exec_fault, adjust_hugepage; bool device = false; unsigned long mmu_seq; struct kvm *kvm = vcpu->kvm; @@ -872,12 +872,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, mark_page_dirty(kvm, gfn); } - if (fault_status != FSC_PERM && !device) + /* + * There is no necessity to perform cache maintenance operations if we + * will only replace the existing table mappings with a block mapping. + */ + adjust_hugepage = fault_granule < vma_pagesize ? true : false; + if (fault_status != FSC_PERM && !device && !adjust_hugepage) clean_dcache_guest_page(pfn, vma_pagesize); if (exec_fault) { prot |= KVM_PGTABLE_PROT_X; - invalidate_icache_guest_page(pfn, vma_pagesize); + if (!adjust_hugepage) + invalidate_icache_guest_page(pfn, vma_pagesize); } if (device)
After dirty-logging is stopped for a VM configured with huge mappings, KVM will recover the table mappings back to block mappings. As we only replace the existing page tables with a block entry and the cacheability has not been changed, the cache maintenance opreations can be skipped. Signed-off-by: Yanan Wang <wangyanan55@huawei.com> --- arch/arm64/kvm/mmu.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)