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| author | Paolo Bonzini <pbonzini@redhat.com> | 2018-07-27 17:44:41 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2018-08-06 17:59:07 +0200 |
| commit | b9b33da2aa7429b0f61bcd218d34e1a277459fb4 (patch) | |
| tree | e96543535148bb56df1d33bcfdd4886108005121 /virt | |
| parent | 877ad952be3d51445f6a74dd63708a9327c8f19d (diff) | |
| download | linux-b9b33da2aa7429b0f61bcd218d34e1a277459fb4.tar.gz | |
KVM: try __get_user_pages_fast even if not in atomic context
We are currently cutting hva_to_pfn_fast short if we do not want an
immediate exit, which is represented by !async && !atomic. However,
this is unnecessary, and __get_user_pages_fast is *much* faster
because the regular get_user_pages takes pmd_lock/pte_lock.
In fact, when many CPUs take a nested vmexit at the same time
the contention on those locks is visible, and this patch removes
about 25% (compared to 4.18) from vmexit.flat on a 16 vCPU
nested guest.
Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 14 |
1 files changed, 6 insertions, 8 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 74544d20bbf8..f83239ac8be1 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1343,18 +1343,16 @@ static inline int check_user_page_hwpoison(unsigned long addr) } /* - * The atomic path to get the writable pfn which will be stored in @pfn, - * true indicates success, otherwise false is returned. + * The fast path to get the writable pfn which will be stored in @pfn, + * true indicates success, otherwise false is returned. It's also the + * only part that runs if we can are in atomic context. */ -static bool hva_to_pfn_fast(unsigned long addr, bool atomic, bool *async, - bool write_fault, bool *writable, kvm_pfn_t *pfn) +static bool hva_to_pfn_fast(unsigned long addr, bool write_fault, + bool *writable, kvm_pfn_t *pfn) { struct page *page[1]; int npages; - if (!(async || atomic)) - return false; - /* * Fast pin a writable pfn only if it is a write fault request * or the caller allows to map a writable pfn for a read fault @@ -1498,7 +1496,7 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async, /* we can do it either atomically or asynchronously, not both */ BUG_ON(atomic && async); - if (hva_to_pfn_fast(addr, atomic, async, write_fault, writable, &pfn)) + if (hva_to_pfn_fast(addr, write_fault, writable, &pfn)) return pfn; if (atomic) |