From: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
To: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
Cc: linux-arch@vger.kernel.org, x86@kernel.org, arnd@arndb.de,
kvm@vger.kernel.org, kvm-ia64@vger.kernel.org,
fernando@oss.ntt.co.jp, mtosatti@redhat.com, agraf@suse.de,
kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org,
yoshikawa.takuya@oss.ntt.co.jp, linuxppc-dev@ozlabs.org,
mingo@redhat.com, paulus@samba.org, avi@redhat.com,
hpa@zytor.com, tglx@linutronix.de
Subject: [RFC][PATCH 1/12 applied today] KVM: x86: avoid unnecessary bitmap allocation when memslot is clean
Date: Tue, 4 May 2010 21:58:54 +0900 [thread overview]
Message-ID: <20100504215854.cd46c959.takuya.yoshikawa@gmail.com> (raw)
In-Reply-To: <20100504215645.6448af8f.takuya.yoshikawa@gmail.com>
Although we always allocate a new dirty bitmap in x86's get_dirty_log(),
it is only used as a zero-source of copy_to_user() and freed right after
that when memslot is clean. This patch uses clear_user() instead of doing
this unnecessary zero-source allocation.
Performance improvement: as we can expect easily, the time needed to
allocate a bitmap is completely reduced. Furthermore, we can avoid the
tlb flush triggered by vmalloc() and get some good effects. In my test,
the improved ioctl was about 4 to 10 times faster than the original one
for clean slots.
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
---
arch/x86/kvm/x86.c | 37 +++++++++++++++++++++++--------------
1 files changed, 23 insertions(+), 14 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6b2ce1d..b95a211 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2744,7 +2744,6 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
struct kvm_memory_slot *memslot;
unsigned long n;
unsigned long is_dirty = 0;
- unsigned long *dirty_bitmap = NULL;
mutex_lock(&kvm->slots_lock);
@@ -2759,27 +2758,30 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
n = kvm_dirty_bitmap_bytes(memslot);
- r = -ENOMEM;
- dirty_bitmap = vmalloc(n);
- if (!dirty_bitmap)
- goto out;
- memset(dirty_bitmap, 0, n);
-
for (i = 0; !is_dirty && i < n/sizeof(long); i++)
is_dirty = memslot->dirty_bitmap[i];
/* If nothing is dirty, don't bother messing with page tables. */
if (is_dirty) {
struct kvm_memslots *slots, *old_slots;
+ unsigned long *dirty_bitmap;
spin_lock(&kvm->mmu_lock);
kvm_mmu_slot_remove_write_access(kvm, log->slot);
spin_unlock(&kvm->mmu_lock);
- slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
- if (!slots)
- goto out_free;
+ r = -ENOMEM;
+ dirty_bitmap = vmalloc(n);
+ if (!dirty_bitmap)
+ goto out;
+ memset(dirty_bitmap, 0, n);
+ r = -ENOMEM;
+ slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
+ if (!slots) {
+ vfree(dirty_bitmap);
+ goto out;
+ }
memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
slots->memslots[log->slot].dirty_bitmap = dirty_bitmap;
@@ -2788,13 +2790,20 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
synchronize_srcu_expedited(&kvm->srcu);
dirty_bitmap = old_slots->memslots[log->slot].dirty_bitmap;
kfree(old_slots);
+
+ r = -EFAULT;
+ if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n)) {
+ vfree(dirty_bitmap);
+ goto out;
+ }
+ vfree(dirty_bitmap);
+ } else {
+ r = -EFAULT;
+ if (clear_user(log->dirty_bitmap, n))
+ goto out;
}
r = 0;
- if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n))
- r = -EFAULT;
-out_free:
- vfree(dirty_bitmap);
out:
mutex_unlock(&kvm->slots_lock);
return r;
--
1.7.0.4
next prev parent reply other threads:[~2010-05-04 12:58 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-04 12:56 [RFC][PATCH 0/12] KVM, x86, ppc, asm-generic: moving dirty bitmaps to user space Takuya Yoshikawa
2010-05-04 12:58 ` Takuya Yoshikawa [this message]
2010-05-04 13:00 ` [RFC][PATCH 2/12] KVM: introduce slot level dirty state management Takuya Yoshikawa
2010-05-04 13:01 ` [RFC][PATCH 3/12] KVM: introduce wrapper functions to create and destroy dirty bitmaps Takuya Yoshikawa
2010-05-04 13:02 ` [RFC][PATCH 4/12] x86: introduce copy_in_user() for 32-bit Takuya Yoshikawa
2010-05-04 13:02 ` [RFC][PATCH 5/12] x86: introduce __set_bit() like function for bitmaps in user space Takuya Yoshikawa
2010-05-04 13:03 ` [RFC][PATCH 6/12 not tested yet] PPC: introduce copy_in_user() for 32-bit Takuya Yoshikawa
2010-05-04 13:04 ` [RFC][PATCH 7/12 not tested yet] PPC: introduce __set_bit() like function for bitmaps in user space Takuya Yoshikawa
2010-05-11 16:00 ` Alexander Graf
2010-05-12 9:25 ` Takuya Yoshikawa
2010-05-04 13:05 ` [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit offset macro Takuya Yoshikawa
2010-05-04 15:03 ` Arnd Bergmann
2010-05-04 16:08 ` Avi Kivity
2010-05-05 2:59 ` Takuya Yoshikawa
2010-05-06 13:38 ` Arnd Bergmann
2010-05-10 11:46 ` Takuya Yoshikawa
2010-05-10 12:01 ` Avi Kivity
2010-05-10 12:01 ` Arnd Bergmann
2010-05-10 12:09 ` Takuya Yoshikawa
2010-05-04 13:06 ` [RFC][PATCH 9/12] KVM: introduce a wrapper function of set_bit_user_non_atomic() Takuya Yoshikawa
2010-05-04 13:07 ` [RFC][PATCH RFC 10/12] KVM: move dirty bitmaps to user space Takuya Yoshikawa
2010-05-11 3:28 ` Marcelo Tosatti
2010-05-12 6:27 ` Takuya Yoshikawa
2010-05-04 13:08 ` [RFC][PATCH 11/12] KVM: introduce new API for getting/switching dirty bitmaps Takuya Yoshikawa
2010-05-11 3:43 ` Marcelo Tosatti
2010-05-11 5:53 ` Takuya Yoshikawa
2010-05-11 14:07 ` Marcelo Tosatti
2010-05-12 6:03 ` Takuya Yoshikawa
2010-05-04 13:11 ` [RFC][PATCH 12/12 sample] qemu-kvm: use " Takuya Yoshikawa
2010-05-10 12:06 ` [RFC][PATCH 0/12] KVM, x86, ppc, asm-generic: moving dirty bitmaps to user space Avi Kivity
2010-05-10 12:26 ` Takuya Yoshikawa
2010-05-11 10:11 ` Takuya Yoshikawa
2010-05-13 11:47 ` Avi Kivity
2010-05-17 9:06 ` Takuya Yoshikawa
2010-05-11 15:55 ` Alexander Graf
2010-05-12 9:19 ` Takuya Yoshikawa
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