From: Paolo Bonzini <pbonzini@redhat.com>
To: Ben Gardon <bgardon@google.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Peter Xu <peterx@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Peter Shier <pshier@google.com>,
Peter Feiner <pfeiner@google.com>,
Junaid Shahid <junaids@google.com>,
Jim Mattson <jmattson@google.com>,
Yulei Zhang <yulei.kernel@gmail.com>,
Wanpeng Li <kernellwp@gmail.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Xiao Guangrong <xiaoguangrong.eric@gmail.com>
Subject: Re: [PATCH v2 00/28] Allow parallel MMU operations with TDP MMU
Date: Wed, 3 Feb 2021 12:00:00 +0100 [thread overview]
Message-ID: <298548e9-ead2-5770-7ae8-e501c9c17263@redhat.com> (raw)
In-Reply-To: <20210202185734.1680553-1-bgardon@google.com>
On 02/02/21 19:57, Ben Gardon wrote:
> The TDP MMU was implemented to simplify and improve the performance of
> KVM's memory management on modern hardware with TDP (EPT / NPT). To build
> on the existing performance improvements of the TDP MMU, add the ability
> to handle vCPU page faults, enabling and disabling dirty logging, and
> removing mappings, in parallel. In the current implementation,
> vCPU page faults (actually EPT/NPT violations/misconfigurations) are the
> largest source of MMU lock contention on VMs with many vCPUs. This
> contention, and the resulting page fault latency, can soft-lock guests
> and degrade performance. Handling page faults in parallel is especially
> useful when booting VMs, enabling dirty logging, and handling demand
> paging. In all these cases vCPUs are constantly incurring page faults on
> each new page accessed.
>
> Broadly, the following changes were required to allow parallel page
> faults (and other MMU operations):
> -- Contention detection and yielding added to rwlocks to bring them up to
> feature parity with spin locks, at least as far as the use of the MMU
> lock is concerned.
> -- TDP MMU page table memory is protected with RCU and freed in RCU
> callbacks to allow multiple threads to operate on that memory
> concurrently.
> -- The MMU lock was changed to an rwlock on x86. This allows the page
> fault handlers to acquire the MMU lock in read mode and handle page
> faults in parallel, and other operations to maintain exclusive use of
> the lock by acquiring it in write mode.
> -- An additional lock is added to protect some data structures needed by
> the page fault handlers, for relatively infrequent operations.
> -- The page fault handler is modified to use atomic cmpxchgs to set SPTEs
> and some page fault handler operations are modified slightly to work
> concurrently with other threads.
>
> This series also contains a few bug fixes and optimizations, related to
> the above, but not strictly part of enabling parallel page fault handling.
>
> Correctness testing:
> The following tests were performed with an SMP kernel and DBX kernel on an
> Intel Skylake machine. The tests were run both with and without the TDP
> MMU enabled.
> -- This series introduces no new failures in kvm-unit-tests
> SMP + no TDP MMU no new failures
> SMP + TDP MMU no new failures
> DBX + no TDP MMU no new failures
> DBX + TDP MMU no new failures
What's DBX? Lockdep etc.?
> -- All KVM selftests behave as expected
> SMP + no TDP MMU all pass except ./x86_64/vmx_preemption_timer_test
> SMP + TDP MMU all pass except ./x86_64/vmx_preemption_timer_test
> (./x86_64/vmx_preemption_timer_test also fails without this patch set,
> both with the TDP MMU on and off.)
Yes, it's flaky. It depends on your host.
> DBX + no TDP MMU all pass
> DBX + TDP MMU all pass
> -- A VM can be booted running a Debian 9 and all memory accessed
> SMP + no TDP MMU works
> SMP + TDP MMU works
> DBX + no TDP MMU works
> DBX + TDP MMU works
>
> This series can be viewed in Gerrit at:
> https://linux-review.googlesource.com/c/linux/kernel/git/torvalds/linux/+/7172
Looks good! I'll wait for a few days of reviews, but I'd like to queue
this for 5.12 and I plan to make it the default in 5.13 or 5.12-rc
(depending on when I can ask Red Hat QE to give it a shake).
It also needs more documentation though. I'll do that myself based on
your KVM Forum talk so that I can teach myself more of it.
Paolo
next prev parent reply other threads:[~2021-02-03 11:02 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-02 18:57 [PATCH v2 00/28] Allow parallel MMU operations with TDP MMU Ben Gardon
2021-02-02 18:57 ` [PATCH v2 01/28] KVM: x86/mmu: change TDP MMU yield function returns to match cond_resched Ben Gardon
2021-02-02 18:57 ` [PATCH v2 02/28] KVM: x86/mmu: Add comment on __tdp_mmu_set_spte Ben Gardon
2021-02-02 18:57 ` [PATCH v2 03/28] KVM: x86/mmu: Add lockdep when setting a TDP MMU SPTE Ben Gardon
2021-02-02 18:57 ` [PATCH v2 04/28] KVM: x86/mmu: Don't redundantly clear TDP MMU pt memory Ben Gardon
2021-02-02 18:57 ` [PATCH v2 05/28] KVM: x86/mmu: Factor out handling of removed page tables Ben Gardon
2021-02-02 18:57 ` [PATCH v2 06/28] locking/rwlocks: Add contention detection for rwlocks Ben Gardon
2021-02-09 20:39 ` Guenter Roeck
2021-02-09 21:46 ` Waiman Long
2021-02-09 22:25 ` Guenter Roeck
2021-02-10 0:27 ` Waiman Long
2021-02-10 0:41 ` Waiman Long
2021-02-10 6:04 ` Guenter Roeck
2021-02-10 14:57 ` Waiman Long
2021-02-10 3:32 ` Waiman Long
2021-02-10 15:15 ` Waiman Long
2021-02-02 18:57 ` [PATCH v2 07/28] sched: Add needbreak " Ben Gardon
2021-02-02 18:57 ` [PATCH v2 08/28] sched: Add cond_resched_rwlock Ben Gardon
2021-02-02 18:57 ` [PATCH v2 09/28] KVM: x86/mmu: Fix braces in kvm_recover_nx_lpages Ben Gardon
2021-02-02 18:57 ` [PATCH v2 10/28] KVM: x86/mmu: Fix TDP MMU zap collapsible SPTEs Ben Gardon
2021-02-03 9:43 ` Paolo Bonzini
2021-02-02 18:57 ` [PATCH v2 11/28] KVM: x86/mmu: Merge flush and non-flush tdp_mmu_iter_cond_resched Ben Gardon
2021-02-02 18:57 ` [PATCH v2 12/28] KVM: x86/mmu: Rename goal_gfn to next_last_level_gfn Ben Gardon
2021-02-02 18:57 ` [PATCH v2 13/28] KVM: x86/mmu: Ensure forward progress when yielding in TDP MMU iter Ben Gardon
2021-02-05 23:42 ` Sean Christopherson
2021-02-02 18:57 ` [PATCH v2 14/28] KVM: x86/mmu: Yield in TDU MMU iter even if no SPTES changed Ben Gardon
2021-02-02 18:57 ` [PATCH v2 15/28] KVM: x86/mmu: Skip no-op changes in TDP MMU functions Ben Gardon
2021-02-02 18:57 ` [PATCH v2 16/28] KVM: x86/mmu: Clear dirtied pages mask bit before early break Ben Gardon
2021-02-02 18:57 ` [PATCH v2 17/28] KVM: x86/mmu: Protect TDP MMU page table memory with RCU Ben Gardon
2021-02-02 18:57 ` [PATCH v2 18/28] KVM: x86/mmu: Use an rwlock for the x86 MMU Ben Gardon
2021-02-02 18:57 ` [PATCH v2 19/28] KVM: x86/mmu: Factor out functions to add/remove TDP MMU pages Ben Gardon
2021-02-02 18:57 ` [PATCH v2 20/28] KVM: x86/mmu: Use atomic ops to set SPTEs in TDP MMU map Ben Gardon
2021-02-03 2:48 ` kernel test robot
2021-02-03 11:14 ` Paolo Bonzini
2021-02-06 0:26 ` Sean Christopherson
2021-02-08 10:32 ` Paolo Bonzini
2021-04-01 10:32 ` Paolo Bonzini
2021-04-01 16:50 ` Ben Gardon
2021-04-01 17:32 ` Paolo Bonzini
2021-04-01 18:09 ` Sean Christopherson
2021-02-02 18:57 ` [PATCH v2 21/28] KVM: x86/mmu: Flush TLBs after zap in TDP MMU PF handler Ben Gardon
2021-02-06 0:29 ` Sean Christopherson
2021-02-02 18:57 ` [PATCH v2 22/28] KVM: x86/mmu: Mark SPTEs in disconnected pages as removed Ben Gardon
2021-02-03 11:17 ` Paolo Bonzini
2021-02-02 18:57 ` [PATCH v2 23/28] KVM: x86/mmu: Allow parallel page faults for the TDP MMU Ben Gardon
2021-02-03 12:39 ` Paolo Bonzini
2021-02-03 17:46 ` Ben Gardon
2021-02-03 18:30 ` Paolo Bonzini
2021-02-06 0:12 ` Sean Christopherson
2021-02-02 18:57 ` [PATCH v2 24/28] KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock Ben Gardon
2021-02-03 11:25 ` Paolo Bonzini
2021-02-03 11:26 ` Paolo Bonzini
2021-02-03 18:31 ` Ben Gardon
2021-02-03 18:32 ` Paolo Bonzini
2021-02-02 18:57 ` [PATCH v2 25/28] KVM: x86/mmu: Allow zapping collapsible SPTEs to use MMU " Ben Gardon
2021-02-03 11:34 ` Paolo Bonzini
2021-02-03 18:51 ` Ben Gardon
2021-02-02 18:57 ` [PATCH v2 26/28] KVM: x86/mmu: Allow enabling / disabling dirty logging under " Ben Gardon
2021-02-03 11:38 ` Paolo Bonzini
2021-02-02 18:57 ` [PATCH v2 27/28] KVM: selftests: Add backing src parameter to dirty_log_perf_test Ben Gardon
2021-02-02 18:57 ` [PATCH v2 28/28] KVM: selftests: Disable dirty logging with vCPUs running Ben Gardon
2021-02-03 10:07 ` Paolo Bonzini
2021-02-03 11:00 ` Paolo Bonzini [this message]
2021-02-03 17:54 ` [PATCH v2 00/28] Allow parallel MMU operations with TDP MMU Sean Christopherson
2021-02-03 18:13 ` Paolo Bonzini
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