Re: [Xen-devel] [PATCH v2 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently
On 03/07/2019 18:02, Nadav Amit wrote: >> On Jul 3, 2019, at 7:04 AM, Juergen Gross wrote: >> >> On 03.07.19 01:51, Nadav Amit wrote: >>> To improve TLB shootdown performance, flush the remote and local TLBs >>> concurrently. Introduce flush_tlb_multi() that does so. Introduce >>> paravirtual versions of flush_tlb_multi() for KVM, Xen and hyper-v (Xen >>> and hyper-v are only compile-tested). >>> While the updated smp infrastructure is capable of running a function on >>> a single local core, it is not optimized for this case. The multiple >>> function calls and the indirect branch introduce some overhead, and >>> might make local TLB flushes slower than they were before the recent >>> changes. >>> Before calling the SMP infrastructure, check if only a local TLB flush >>> is needed to restore the lost performance in this common case. This >>> requires to check mm_cpumask() one more time, but unless this mask is >>> updated very frequently, this should impact performance negatively. >>> Cc: "K. Y. Srinivasan" >>> Cc: Haiyang Zhang >>> Cc: Stephen Hemminger >>> Cc: Sasha Levin >>> Cc: Thomas Gleixner >>> Cc: Ingo Molnar >>> Cc: Borislav Petkov >>> Cc: x...@kernel.org >>> Cc: Juergen Gross >>> Cc: Paolo Bonzini >>> Cc: Dave Hansen >>> Cc: Andy Lutomirski >>> Cc: Peter Zijlstra >>> Cc: Boris Ostrovsky >>> Cc: linux-hyp...@vger.kernel.org >>> Cc: linux-ker...@vger.kernel.org >>> Cc: virtualization@lists.linux-foundation.org >>> Cc: k...@vger.kernel.org >>> Cc: xen-de...@lists.xenproject.org >>> Signed-off-by: Nadav Amit >>> --- >>> arch/x86/hyperv/mmu.c | 13 +++--- >>> arch/x86/include/asm/paravirt.h | 6 +-- >>> arch/x86/include/asm/paravirt_types.h | 4 +- >>> arch/x86/include/asm/tlbflush.h | 9 ++-- >>> arch/x86/include/asm/trace/hyperv.h | 2 +- >>> arch/x86/kernel/kvm.c | 11 +++-- >>> arch/x86/kernel/paravirt.c| 2 +- >>> arch/x86/mm/tlb.c | 65 --- >>> arch/x86/xen/mmu_pv.c | 20 ++--- >>> include/trace/events/xen.h| 2 +- >>> 10 files changed, 91 insertions(+), 43 deletions(-) >> ... >> >>> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c >>> index beb44e22afdf..19e481e6e904 100644 >>> --- a/arch/x86/xen/mmu_pv.c >>> +++ b/arch/x86/xen/mmu_pv.c >>> @@ -1355,8 +1355,8 @@ static void xen_flush_tlb_one_user(unsigned long addr) >>> preempt_enable(); >>> } >>> -static void xen_flush_tlb_others(const struct cpumask *cpus, >>> -const struct flush_tlb_info *info) >>> +static void xen_flush_tlb_multi(const struct cpumask *cpus, >>> + const struct flush_tlb_info *info) >>> { >>> struct { >>> struct mmuext_op op; >>> @@ -1366,7 +1366,7 @@ static void xen_flush_tlb_others(const struct cpumask >>> *cpus, >>> const size_t mc_entry_size = sizeof(args->op) + >>> sizeof(args->mask[0]) * BITS_TO_LONGS(num_possible_cpus()); >>> - trace_xen_mmu_flush_tlb_others(cpus, info->mm, info->start, info->end); >>> + trace_xen_mmu_flush_tlb_multi(cpus, info->mm, info->start, info->end); >>> if (cpumask_empty(cpus)) >>> return; /* nothing to do */ >>> @@ -1375,9 +1375,17 @@ static void xen_flush_tlb_others(const struct >>> cpumask *cpus, >>> args = mcs.args; >>> args->op.arg2.vcpumask = to_cpumask(args->mask); >>> - /* Remove us, and any offline CPUS. */ >>> + /* Flush locally if needed and remove us */ >>> + if (cpumask_test_cpu(smp_processor_id(), to_cpumask(args->mask))) { >>> + local_irq_disable(); >>> + flush_tlb_func_local(info); >> I think this isn't the correct function for PV guests. >> >> In fact it should be much easier: just don't clear the own cpu from the >> mask, that's all what's needed. The hypervisor is just fine having the >> current cpu in the mask and it will do the right thing. > Thanks. I will do so in v3. I don’t think Hyper-V people would want to do > the same, unfortunately, since it would induce VM-exit on TLB flushes. Why do you believe the vmexit matters? You're talking one anyway for the IPI. Intel only have virtualised self-IPI, and while AMD do have working non-self IPIs, you still take a vmexit anyway if any destination vcpu isn't currently running in non-root mode (IIRC). At that point, you might as well have the hypervisor do all the hard work via a multi-cpu shootdown/flush hypercall, rather than trying to arrange it locally. ~Andrew ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [Xen-devel] [PATCH v2 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently
> On Jul 3, 2019, at 10:43 AM, Andrew Cooper wrote: > > On 03/07/2019 18:02, Nadav Amit wrote: >>> On Jul 3, 2019, at 7:04 AM, Juergen Gross wrote: >>> >>> On 03.07.19 01:51, Nadav Amit wrote: To improve TLB shootdown performance, flush the remote and local TLBs concurrently. Introduce flush_tlb_multi() that does so. Introduce paravirtual versions of flush_tlb_multi() for KVM, Xen and hyper-v (Xen and hyper-v are only compile-tested). While the updated smp infrastructure is capable of running a function on a single local core, it is not optimized for this case. The multiple function calls and the indirect branch introduce some overhead, and might make local TLB flushes slower than they were before the recent changes. Before calling the SMP infrastructure, check if only a local TLB flush is needed to restore the lost performance in this common case. This requires to check mm_cpumask() one more time, but unless this mask is updated very frequently, this should impact performance negatively. Cc: "K. Y. Srinivasan" Cc: Haiyang Zhang Cc: Stephen Hemminger Cc: Sasha Levin Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: x...@kernel.org Cc: Juergen Gross Cc: Paolo Bonzini Cc: Dave Hansen Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Boris Ostrovsky Cc: linux-hyp...@vger.kernel.org Cc: linux-ker...@vger.kernel.org Cc: virtualization@lists.linux-foundation.org Cc: k...@vger.kernel.org Cc: xen-de...@lists.xenproject.org Signed-off-by: Nadav Amit --- arch/x86/hyperv/mmu.c | 13 +++--- arch/x86/include/asm/paravirt.h | 6 +-- arch/x86/include/asm/paravirt_types.h | 4 +- arch/x86/include/asm/tlbflush.h | 9 ++-- arch/x86/include/asm/trace/hyperv.h | 2 +- arch/x86/kernel/kvm.c | 11 +++-- arch/x86/kernel/paravirt.c| 2 +- arch/x86/mm/tlb.c | 65 --- arch/x86/xen/mmu_pv.c | 20 ++--- include/trace/events/xen.h| 2 +- 10 files changed, 91 insertions(+), 43 deletions(-) >>> ... >>> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c index beb44e22afdf..19e481e6e904 100644 --- a/arch/x86/xen/mmu_pv.c +++ b/arch/x86/xen/mmu_pv.c @@ -1355,8 +1355,8 @@ static void xen_flush_tlb_one_user(unsigned long addr) preempt_enable(); } -static void xen_flush_tlb_others(const struct cpumask *cpus, - const struct flush_tlb_info *info) +static void xen_flush_tlb_multi(const struct cpumask *cpus, + const struct flush_tlb_info *info) { struct { struct mmuext_op op; @@ -1366,7 +1366,7 @@ static void xen_flush_tlb_others(const struct cpumask *cpus, const size_t mc_entry_size = sizeof(args->op) + sizeof(args->mask[0]) * BITS_TO_LONGS(num_possible_cpus()); - trace_xen_mmu_flush_tlb_others(cpus, info->mm, info->start, info->end); + trace_xen_mmu_flush_tlb_multi(cpus, info->mm, info->start, info->end); if (cpumask_empty(cpus)) return; /* nothing to do */ @@ -1375,9 +1375,17 @@ static void xen_flush_tlb_others(const struct cpumask *cpus, args = mcs.args; args->op.arg2.vcpumask = to_cpumask(args->mask); - /* Remove us, and any offline CPUS. */ + /* Flush locally if needed and remove us */ + if (cpumask_test_cpu(smp_processor_id(), to_cpumask(args->mask))) { + local_irq_disable(); + flush_tlb_func_local(info); >>> I think this isn't the correct function for PV guests. >>> >>> In fact it should be much easier: just don't clear the own cpu from the >>> mask, that's all what's needed. The hypervisor is just fine having the >>> current cpu in the mask and it will do the right thing. >> Thanks. I will do so in v3. I don’t think Hyper-V people would want to do >> the same, unfortunately, since it would induce VM-exit on TLB flushes. > > Why do you believe the vmexit matters? You're talking one anyway for > the IPI. > > Intel only have virtualised self-IPI, and while AMD do have working > non-self IPIs, you still take a vmexit anyway if any destination vcpu > isn't currently running in non-root mode (IIRC). > > At that point, you might as well have the hypervisor do all the hard > work via a multi-cpu shootdown/flush hypercall, rather than trying to > arrange it locally. I forgot that xen_flush_tlb_multi() should actually only be called when there are some remote CPUs (as I optimized the case in which there is only a single local CPU that needs to be flushed), so you are right. ___ Virtualization mailing list Virtualization@lists.lin