[Xen-changelog] [linux-2.6.18-xen] drivers/xen/blkback: Add the kernel side of the blkback queueing feature.

["Xen patchbot-linux-2.6.18-xen" <patchbot-linux-2.6.18-xen@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1250267323 -3600
# Node ID 56df01ffed10fa046ee7ddd65e439a131166944a
# Parent  74e670203038a774f85c31b04c8e0e0fecbef60d
drivers/xen/blkback: Add the kernel side of the blkback queueing feature.

This is similar to the credit scheduler used in netif, except that it
allows occasional burstability (for use with e2fsck as an example).

Signed-off-by: William Pitcock <nenolod@xxxxxxxxxxxxxxxx>
---
 drivers/xen/blkback/blkback.c |   25 +++++++++++++++++++++++++
 drivers/xen/blkback/common.h  |    5 +++++
 drivers/xen/blkback/xenbus.c  |   41 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+)

diff -r 74e670203038 -r 56df01ffed10 drivers/xen/blkback/blkback.c
--- a/drivers/xen/blkback/blkback.c     Fri Aug 14 17:05:54 2009 +0100
+++ b/drivers/xen/blkback/blkback.c     Fri Aug 14 17:28:43 2009 +0100
@@ -200,6 +200,16 @@ static void print_stats(blkif_t *blkif)
        blkif->st_oo_req = 0;
 }
 
+static void refill_credit(blkif_t *blkif)
+{
+       blkif->credit_time = jiffies + msecs_to_jiffies(blkif->credit_msec);
+       blkif->available_credit += blkif->credit_req;
+
+       /* this allows for bursting. */
+       if (blkif->available_credit > (blkif->credit_req * blkif->credit_msec))
+               blkif->available_credit = blkif->credit_req;
+}
+
 int blkif_schedule(void *arg)
 {
        blkif_t *blkif = arg;
@@ -226,6 +236,9 @@ int blkif_schedule(void *arg)
                if (do_block_io_op(blkif))
                        blkif->waiting_reqs = 1;
                unplug_queue(blkif);
+
+               if (time_after(jiffies, blkif->credit_time))
+                       refill_credit(blkif);
 
                if (log_stats && time_after(jiffies, blkif->st_print))
                        print_stats(blkif);
@@ -313,10 +326,22 @@ static int do_block_io_op(blkif_t *blkif
        rp = blk_rings->common.sring->req_prod;
        rmb(); /* Ensure we see queued requests up to 'rp'. */
 
+       /* if there's no available request credit right now, and limiting
+        * is requested, then don't bother with going any further.
+        */
+       if (blkif->remaining_credit <= 0 && blkif->credit_req != 0)
+               return (rc != rp) ? 1 : 0;
+
        while (rc != rp) {
 
                if (RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rc))
                        break;
+
+               /* FIXME: Should we report QoS overages as VBD_OO, or not? */
+               if (blkif->credit_req != 0 && --blkif->remaining_credit <= 0) {
+                       more_to_do = 1;
+                       break;
+               }
 
                if (kthread_should_stop()) {
                        more_to_do = 1;
diff -r 74e670203038 -r 56df01ffed10 drivers/xen/blkback/common.h
--- a/drivers/xen/blkback/common.h      Fri Aug 14 17:05:54 2009 +0100
+++ b/drivers/xen/blkback/common.h      Fri Aug 14 17:28:43 2009 +0100
@@ -96,6 +96,11 @@ typedef struct blkif_st {
 
        grant_handle_t shmem_handle;
        grant_ref_t    shmem_ref;
+
+       int                 credit_req;
+       int                 remaining_credit;
+       int                 credit_msec;
+       unsigned long       credit_time;
 } blkif_t;
 
 blkif_t *blkif_alloc(domid_t domid);
diff -r 74e670203038 -r 56df01ffed10 drivers/xen/blkback/xenbus.c
--- a/drivers/xen/blkback/xenbus.c      Fri Aug 14 17:05:54 2009 +0100
+++ b/drivers/xen/blkback/xenbus.c      Fri Aug 14 17:28:43 2009 +0100
@@ -255,6 +255,42 @@ fail:
        return err;
 }
 
+static void blkback_read_credit(struct xenbus_transaction xbt,
+                               struct xenbus_device *dev,
+                                unsigned long *credit, unsigned long *msec)
+{
+       char *s, *e;
+       unsigned long b, u;
+       char *ratestr;
+
+       /* Default to unlimited I/O operations. */
+       *credit = ~0UL;
+       *usec = 0;
+
+       ratestr = xenbus_read(xbt, dev->nodename, "credit", NULL);
+       if (IS_ERR(ratestr))
+               return;
+
+       s = ratestr;
+       b = simple_strtoul(s, &e, 10);
+       if ((s == e) || (*e != ','))
+               goto fail;
+
+       s = e + 1;
+       u = simple_strtoul(s, &e, 10);
+       if ((s == e) || (*e != '\0'))
+               goto fail;
+
+       *credit = b;
+       *msec = (u / 1000);
+
+       kfree(ratestr);
+       return;
+
+ fail:
+       WPRINTK("Failed to parse I/O credit limit. I/O operations are 
unlimited.\n");
+       kfree(ratestr);
+}
 
 /**
  * Callback received when the hotplug scripts have placed the physical-device
@@ -401,6 +437,7 @@ static void frontend_changed(struct xenb
 /* ** Connection ** */
 
 
+
 /**
  * Write the physical details regarding the block device to the store, and
  * switch to Connected state.
@@ -424,6 +461,10 @@ again:
        err = blkback_barrier(xbt, be, 1);
        if (err)
                goto abort;
+
+       blkback_read_credit(xbt, dev, &be->blkif->credit_req,
+                           &be->blkif->credit_msec);
+       be->blkif->remaining_credit = be->blkif->credit_req;
 
        err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
                            vbd_size(&be->blkif->vbd));

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