[PATCH v2 3/6] vhost: add per VQ memory region caching

[Igor Mammedov]

that brings down translate_desc() cost to around 210ns
if accessed descriptors are from the same memory region.

Signed-off-by: Igor Mammedov <imamm...@redhat.com>
---
that's what netperf/iperf workloads were during testing.
---
 drivers/vhost/vhost.c | 16 +++++++++++++---
 drivers/vhost/vhost.h |  1 +
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 99931a0..5c39a1e 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -200,6 +200,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
        vq->call = NULL;
        vq->log_ctx = NULL;
        vq->memory = NULL;
+       vq->cached_reg = 0;
 }
 
 static int vhost_worker(void *data)
@@ -649,6 +650,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct 
vhost_memory __user *m)
        for (i = 0; i < d->nvqs; ++i) {
                mutex_lock(&d->vqs[i]->mutex);
                d->vqs[i]->memory = newmem;
+               d->vqs[i]->cached_reg = 0;
                mutex_unlock(&d->vqs[i]->mutex);
        }
        kvfree(oldmem);
@@ -936,11 +938,17 @@ done:
 EXPORT_SYMBOL_GPL(vhost_dev_ioctl);
 
 static const struct vhost_memory_region *find_region(struct vhost_memory *mem,
-                                                    __u64 addr, __u32 len)
+                                                    __u64 addr, __u32 len,
+                                                    int *cached_reg)
 {
        const struct vhost_memory_region *reg;
        int start = 0, end = mem->nregions;
 
+       reg = mem->regions + *cached_reg;
+       if (likely(addr >= reg->guest_phys_addr &&
+               reg->guest_phys_addr + reg->memory_size > addr))
+               return reg;
+
        while (start < end) {
                int slot = start + (end - start) / 2;
                reg = mem->regions + slot;
@@ -952,8 +960,10 @@ static const struct vhost_memory_region 
*find_region(struct vhost_memory *mem,
 
        reg = mem->regions + start;
        if (addr >= reg->guest_phys_addr &&
-               reg->guest_phys_addr + reg->memory_size > addr)
+               reg->guest_phys_addr + reg->memory_size > addr) {
+               *cached_reg = start;
                return reg;
+       }
        return NULL;
 }
 
@@ -1107,7 +1117,7 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 
addr, u32 len,
                        ret = -ENOBUFS;
                        break;
                }
-               reg = find_region(mem, addr, len);
+               reg = find_region(mem, addr, len, &vq->cached_reg);
                if (unlikely(!reg)) {
                        ret = -EFAULT;
                        break;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 8c1c792..68bd00f 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -106,6 +106,7 @@ struct vhost_virtqueue {
        /* Log write descriptors */
        void __user *log_base;
        struct vhost_log *log;
+       int cached_reg;
 };
 
 struct vhost_dev {
-- 
1.8.3.1

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