[PATCH 1/4] Hack: measure stack taken by vring from virtio_blk

[Rusty Russell]

Results (x86-64, Minchan's .config):

gcc 4.8.2: virtio_blk: stack used = 392
gcc 4.6.4: virtio_blk: stack used = 528

Signed-off-by: Rusty Russell <ru...@rustcorp.com.au>
---
 drivers/block/virtio_blk.c   | 11 ++++++++++-
 drivers/virtio/virtio_ring.c | 11 +++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index cb9b1f8326c3..894e290b4bd2 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -151,15 +151,19 @@ static void virtblk_done(struct virtqueue *vq)
        spin_unlock_irqrestore(&vblk->vq_lock, flags);
 }
 
+extern struct task_struct *record_stack;
+extern unsigned long stack_top;
+
 static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
 {
        struct virtio_blk *vblk = hctx->queue->queuedata;
        struct virtblk_req *vbr = req->special;
        unsigned long flags;
        unsigned int num;
+       unsigned long stack_bottom;
        const bool last = (req->cmd_flags & REQ_END) != 0;
        int err;
-
+       
        BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
 
        vbr->req = req;
@@ -199,7 +203,12 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, 
struct request *req)
        }
 
        spin_lock_irqsave(&vblk->vq_lock, flags);
+       record_stack = current;
+       __asm__ __volatile__("movq %%rsp,%0" : "=g" (stack_bottom));
        err = __virtblk_add_req(vblk->vq, vbr, vbr->sg, num);
+       record_stack = NULL;
+
+       printk("virtio_blk: stack used = %lu\n", stack_bottom - stack_top);
        if (err) {
                virtqueue_kick(vblk->vq);
                blk_mq_stop_hw_queue(hctx);
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 4d08f45a9c29..f6ad99ffdc40 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -54,6 +54,14 @@
 #define END_USE(vq)
 #endif
 
+extern struct task_struct *record_stack;
+struct task_struct *record_stack;
+EXPORT_SYMBOL(record_stack);
+
+extern unsigned long stack_top;
+unsigned long stack_top;
+EXPORT_SYMBOL(stack_top);
+
 struct vring_virtqueue
 {
        struct virtqueue vq;
@@ -137,6 +145,9 @@ static inline int vring_add_indirect(struct vring_virtqueue 
*vq,
         */
        gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);
 
+       if (record_stack == current)
+               __asm__ __volatile__("movq %%rsp,%0" : "=g" (stack_top));
+
        desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
        if (!desc)
                return -ENOMEM;
-- 
1.9.1

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