| Message ID | 50FFB658.6040205@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Jan 23, 2013 at 06:07:20PM +0800, Xiao Guangrong wrote: > It makes set_spte more clean and reduces branch prediction > > Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> > --- > arch/x86/kvm/mmu.c | 37 ++++++++++++++++++++++++++----------- > 1 files changed, 26 insertions(+), 11 deletions(-) Don't see set_spte as being a performance problem? IMO the current code is quite simple. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/25/2013 08:15 AM, Marcelo Tosatti wrote: > On Wed, Jan 23, 2013 at 06:07:20PM +0800, Xiao Guangrong wrote: >> It makes set_spte more clean and reduces branch prediction >> >> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> >> --- >> arch/x86/kvm/mmu.c | 37 ++++++++++++++++++++++++++----------- >> 1 files changed, 26 insertions(+), 11 deletions(-) > > Don't see set_spte as being a performance problem? > IMO the current code is quite simple. Yes, this is not a performance problem. I just dislike this many continuous "if"-s in the function: if (xxx) xxx if (xxx) xxx .... Totally, it has 7 "if"-s before this patch. Okay, if you think this is unnecessary, i will drop this patch. :) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Jan 25, 2013 at 10:46:31AM +0800, Xiao Guangrong wrote: > On 01/25/2013 08:15 AM, Marcelo Tosatti wrote: > > On Wed, Jan 23, 2013 at 06:07:20PM +0800, Xiao Guangrong wrote: > >> It makes set_spte more clean and reduces branch prediction > >> > >> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> > >> --- > >> arch/x86/kvm/mmu.c | 37 ++++++++++++++++++++++++++----------- > >> 1 files changed, 26 insertions(+), 11 deletions(-) > > > > Don't see set_spte as being a performance problem? > > IMO the current code is quite simple. > > Yes, this is not a performance problem. > > I just dislike this many continuous "if"-s in the function: > > if (xxx) > xxx > if (xxx) > xxx > .... > > Totally, it has 7 "if"-s before this patch. > > Okay, if you think this is unnecessary, i will drop this patch. :) Yes, please (unless you can show set_spte is a performance problem). -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Jan 28, 2013 at 10:07:15PM -0200, Marcelo Tosatti wrote: > On Fri, Jan 25, 2013 at 10:46:31AM +0800, Xiao Guangrong wrote: > > On 01/25/2013 08:15 AM, Marcelo Tosatti wrote: > > > On Wed, Jan 23, 2013 at 06:07:20PM +0800, Xiao Guangrong wrote: > > >> It makes set_spte more clean and reduces branch prediction > > >> > > >> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> > > >> --- > > >> arch/x86/kvm/mmu.c | 37 ++++++++++++++++++++++++++----------- > > >> 1 files changed, 26 insertions(+), 11 deletions(-) > > > > > > Don't see set_spte as being a performance problem? > > > IMO the current code is quite simple. > > > > Yes, this is not a performance problem. > > > > I just dislike this many continuous "if"-s in the function: > > > > if (xxx) > > xxx > > if (xxx) > > xxx > > .... > > > > Totally, it has 7 "if"-s before this patch. > > > > Okay, if you think this is unnecessary, i will drop this patch. :) > > Yes, please (unless you can show set_spte is a performance problem). Same thing for spte fast drop: is it a performance problem? Please try to group changes into smaller, less controversial sets with a clear goal: - Debated performance improvement. - Cleanups (eg mmu_set_spte argument removal). - Bug fixes. - Performance improvements. Thanks. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Jan 28, 2013 at 11:07:58PM -0200, Marcelo Tosatti wrote: > On Mon, Jan 28, 2013 at 10:07:15PM -0200, Marcelo Tosatti wrote: > > On Fri, Jan 25, 2013 at 10:46:31AM +0800, Xiao Guangrong wrote: > > > On 01/25/2013 08:15 AM, Marcelo Tosatti wrote: > > > > On Wed, Jan 23, 2013 at 06:07:20PM +0800, Xiao Guangrong wrote: > > > >> It makes set_spte more clean and reduces branch prediction > > > >> > > > >> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> > > > >> --- > > > >> arch/x86/kvm/mmu.c | 37 ++++++++++++++++++++++++++----------- > > > >> 1 files changed, 26 insertions(+), 11 deletions(-) > > > > > > > > Don't see set_spte as being a performance problem? > > > > IMO the current code is quite simple. > > > > > > Yes, this is not a performance problem. > > > > > > I just dislike this many continuous "if"-s in the function: > > > > > > if (xxx) > > > xxx > > > if (xxx) > > > xxx > > > .... > > > > > > Totally, it has 7 "if"-s before this patch. > > > > > > Okay, if you think this is unnecessary, i will drop this patch. :) > > > > Yes, please (unless you can show set_spte is a performance problem). > > Same thing for spte fast drop: is it a performance problem? > I like spte fast drop because it gets rid of "goto restart" pattern. for_each_spte_in_rmap_safe() can be the alternative. > Please try to group changes into smaller, less controversial sets with > a clear goal: > > - Debated performance improvement. > - Cleanups (eg mmu_set_spte argument removal). > - Bug fixes. > - Performance improvements. > > Thanks. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/29/2013 09:07 AM, Marcelo Tosatti wrote: > On Mon, Jan 28, 2013 at 10:07:15PM -0200, Marcelo Tosatti wrote: >> On Fri, Jan 25, 2013 at 10:46:31AM +0800, Xiao Guangrong wrote: >>> On 01/25/2013 08:15 AM, Marcelo Tosatti wrote: >>>> On Wed, Jan 23, 2013 at 06:07:20PM +0800, Xiao Guangrong wrote: >>>>> It makes set_spte more clean and reduces branch prediction >>>>> >>>>> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> >>>>> --- >>>>> arch/x86/kvm/mmu.c | 37 ++++++++++++++++++++++++++----------- >>>>> 1 files changed, 26 insertions(+), 11 deletions(-) >>>> >>>> Don't see set_spte as being a performance problem? >>>> IMO the current code is quite simple. >>> >>> Yes, this is not a performance problem. >>> >>> I just dislike this many continuous "if"-s in the function: >>> >>> if (xxx) >>> xxx >>> if (xxx) >>> xxx >>> .... >>> >>> Totally, it has 7 "if"-s before this patch. >>> >>> Okay, if you think this is unnecessary, i will drop this patch. :) >> >> Yes, please (unless you can show set_spte is a performance problem). > > Same thing for spte fast drop: is it a performance problem? It does not fix a performance problem. The patch does optimization on the noncrucial path and cleanup for the previous patch. > > Please try to group changes into smaller, less controversial sets with > a clear goal: Ah. I thought they are simple and most of them have been reviewed, so i putted them into one group, now i know i made a mistake. ;) > > - Debated performance improvement. > - Cleanups (eg mmu_set_spte argument removal). > - Bug fixes. > - Performance improvements. Okay. I will split the long series into these set: Set 1 for improvement: [PATCH v2 01/12] KVM: MMU: lazily drop large spte Set 2 for cleanups: [PATCH v2 02/12] KVM: MMU: cleanup mapping-level [PATCH v2 07/12] KVM: MMU: remove pt_access in mmu_set_spte [PATCH v2 08/12] KVM: MMU: cleanup __direct_map Set 3 for simplifying set spte path: [PATCH v2 03/12] KVM: MMU: simplify mmu_set_spte [PATCH v2 04/12] KVM: MMU: simplify set_spte [PATCH v2 05/12] KVM: MMU: introduce vcpu_adjust_access Set 4 for fixing and unifying rmap walking [PATCH v2 11/12] KVM: MMU: fix spte assertion [PATCH v2 09/12] KVM: MMU: introduce mmu_spte_establish [PATCH v2 10/12] KVM: MMU: unify the code of walking pte list [PATCH v2 12/12] KVM: MMU: fast drop all spte on the pte_list Thanks! -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 43b7e0c..a8a9c0e 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -235,6 +235,29 @@ static inline u64 rsvd_bits(int s, int e) return ((1ULL << (e - s + 1)) - 1) << s; } +static u64 gaccess_to_spte_access[ACC_ALL + 1]; +static void build_access_table(void) +{ + int access; + + for (access = 0; access < ACC_ALL + 1; access++) { + u64 spte_access = 0; + + if (access & ACC_EXEC_MASK) + spte_access |= shadow_x_mask; + else + spte_access |= shadow_nx_mask; + + if (access & ACC_USER_MASK) + spte_access |= shadow_user_mask; + + if (access & ACC_WRITE_MASK) + spte_access |= PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE; + + gaccess_to_spte_access[access] = spte_access; + } +} + void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, u64 dirty_mask, u64 nx_mask, u64 x_mask) { @@ -243,6 +266,7 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, shadow_dirty_mask = dirty_mask; shadow_nx_mask = nx_mask; shadow_x_mask = x_mask; + build_access_table(); } EXPORT_SYMBOL_GPL(kvm_mmu_set_mask_ptes); @@ -2391,20 +2415,11 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, if (!speculative) spte |= shadow_accessed_mask; - if (pte_access & ACC_EXEC_MASK) - spte |= shadow_x_mask; - else - spte |= shadow_nx_mask; - - if (pte_access & ACC_USER_MASK) - spte |= shadow_user_mask; - - if (pte_access & ACC_WRITE_MASK) - spte |= PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE; - if (level > PT_PAGE_TABLE_LEVEL) spte |= PT_PAGE_SIZE_MASK; + spte |= gaccess_to_spte_access[pte_access]; + if (tdp_enabled) spte |= kvm_x86_ops->get_mt_mask(vcpu, gfn, kvm_is_mmio_pfn(pfn));
It makes set_spte more clean and reduces branch prediction Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> --- arch/x86/kvm/mmu.c | 37 ++++++++++++++++++++++++++----------- 1 files changed, 26 insertions(+), 11 deletions(-)