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Tsirkin" , Paolo Bonzini , Sean Christopherson , Yan Zhao , Alex Williamson , Jason Wang , Kevin Kevin , Vitaly Kuznetsov , peterx@redhat.com, "Dr . David Alan Gilbert" Subject: [PATCH v3 02/21] drm/i915/gvt: subsitute kvm_read/write_guest with vfio_iova_rw Date: Thu, 9 Jan 2020 09:57:10 -0500 Message-Id: <20200109145729.32898-3-peterx@redhat.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200109145729.32898-1-peterx@redhat.com> References: <20200109145729.32898-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yan Zhao As a device model, it is better to read/write guest memory using vfio interface, so that vfio is able to maintain dirty info of device IOVAs. Compared to CPU side interfaces kvm_read/write_guest(), vfio_iova_rw() has ~600 cycles more overhead on average. ------------------------------------- | interface | avg cpu cycles | |-----------------------------------| | kvm_write_guest | 1546 | | ----------------------------------| | kvm_read_guest | 686 | |-----------------------------------| | vfio_iova_rw(w) | 2233 | |-----------------------------------| | vfio_iova_rw(r) | 1262 | ------------------------------------- Comparison of benchmarks scores are as blow: --------------------------------------------------------- | avg score | kvm_read/write_guest | vfio_iova_rw | --------------------------------------------------------- | Glmark2 | 1132 | 1138.2 | --------------------------------------------------------- | Lightsmark | 61.558 | 61.538 | |-------------------------------------------------------- | OpenArena | 142.77 | 136.6 | --------------------------------------------------------- | Heaven | 698 | 686.8 | -------------------------------------------------------- No obvious performance downgrade found. Cc: Kevin Tian Signed-off-by: Yan Zhao [peterx: pass in "write" to vfio_iova_rw(), suggested by Paolo] Signed-off-by: Peter Xu --- drivers/gpu/drm/i915/gvt/kvmgt.c | 25 ++++++------------------- 1 file changed, 6 insertions(+), 19 deletions(-) diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c index 3259a1fa69e1..5fb82f285b98 100644 --- a/drivers/gpu/drm/i915/gvt/kvmgt.c +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c @@ -1968,31 +1968,18 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa, void *buf, unsigned long len, bool write) { struct kvmgt_guest_info *info; - struct kvm *kvm; - int idx, ret; - bool kthread = current->mm == NULL; + int ret; + struct intel_vgpu *vgpu; + struct device *dev; if (!handle_valid(handle)) return -ESRCH; info = (struct kvmgt_guest_info *)handle; - kvm = info->kvm; - - if (kthread) { - if (!mmget_not_zero(kvm->mm)) - return -EFAULT; - use_mm(kvm->mm); - } - - idx = srcu_read_lock(&kvm->srcu); - ret = write ? kvm_write_guest(kvm, gpa, buf, len) : - kvm_read_guest(kvm, gpa, buf, len); - srcu_read_unlock(&kvm->srcu, idx); + vgpu = info->vgpu; + dev = mdev_dev(vgpu->vdev.mdev); - if (kthread) { - unuse_mm(kvm->mm); - mmput(kvm->mm); - } + ret = vfio_iova_rw(dev, gpa, buf, len, write); return ret; } -- 2.24.1