[PATCH 1/4] kvmtool: ARM: force alignment of memory for THP

[Marc Zyngier]

Use of THP requires that the VMA containing the guest memory is
2MB aligned. Unfortunately, nothing in kvmtool ensures that the
memory is actually aligned, making the use of THP very unlikely.

Just follow what we're already doing for virtio, and expand our
forced alignment to 2M.

* without this patch:
root@muffin-man:~# for i in $(seq 1 5); do ./hackbench 50 process 1000; done
Running with 50*40 (== 2000) tasks.
Time: 113.600
Running with 50*40 (== 2000) tasks.
Time: 108.650
Running with 50*40 (== 2000) tasks.
Time: 110.753
Running with 50*40 (== 2000) tasks.
Time: 116.992
Running with 50*40 (== 2000) tasks.
Time: 117.317

* with this patch:
root@muffin-man:~# for i in $(seq 1 5); do ./hackbench 50 process 1000; done
Running with 50*40 (== 2000) tasks.
Time: 97.613
Running with 50*40 (== 2000) tasks.
Time: 96.111
Running with 50*40 (== 2000) tasks.
Time: 97.090
Running with 50*40 (== 2000) tasks.
Time: 100.820
Running with 50*40 (== 2000) tasks.
Time: 100.298

Acked-by: Will Deacon <will.dea...@arm.com>
Signed-off-by: Marc Zyngier <marc.zyng...@arm.com>
---
 tools/kvm/arm/kvm.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/kvm/arm/kvm.c b/tools/kvm/arm/kvm.c
index 008b7fe..d0d64ff 100644
--- a/tools/kvm/arm/kvm.c
+++ b/tools/kvm/arm/kvm.c
@@ -61,11 +61,13 @@ void kvm__arch_set_cmdline(char *cmdline, bool video)
 void kvm__arch_init(struct kvm *kvm, const char *hugetlbfs_path, u64 ram_size)
 {
        /*
-        * Allocate guest memory. We must align out buffer to 64K to
+        * Allocate guest memory. We must align our buffer to 64K to
         * correlate with the maximum guest page size for virtio-mmio.
+        * If using THP, then our minimal alignment becomes 2M.
+        * 2M trumps 64K, so let's go with that.
         */
        kvm->ram_size = min(ram_size, (u64)ARM_MAX_MEMORY(kvm));
-       kvm->arch.ram_alloc_size = kvm->ram_size + SZ_64K;
+       kvm->arch.ram_alloc_size = kvm->ram_size + SZ_2M;
        kvm->arch.ram_alloc_start = mmap_anon_or_hugetlbfs(kvm, hugetlbfs_path,
                                                kvm->arch.ram_alloc_size);
 
@@ -74,7 +76,7 @@ void kvm__arch_init(struct kvm *kvm, const char 
*hugetlbfs_path, u64 ram_size)
                    kvm->arch.ram_alloc_size, errno);
 
        kvm->ram_start = (void *)ALIGN((unsigned long)kvm->arch.ram_alloc_start,
-                                       SZ_64K);
+                                       SZ_2M);
 
        madvise(kvm->arch.ram_alloc_start, kvm->arch.ram_alloc_size,
                MADV_MERGEABLE);
-- 
1.8.3.4

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