Impact: add ability to define I/O usage policies
This enables a nieve token-based QoS system which allows for guests to
get an equal share of I/O requests. Without this patch, a misbehaving or
misconfigured guest can use up any available I/O resources, degrading I/O
performance for other guests on the machine.
The method for specifying these limitations is not implemented in this patch,
because that is an operation detail.
Signed-off-by: William Pitcock <nenolod@xxxxxxxxxxxxxxxx>
---
drivers/xen/blkback/blkback.c | 22 ++++++++++++++++++++++
drivers/xen/blkback/common.h | 6 ++++++
2 files changed, 28 insertions(+), 0 deletions(-)
diff --git a/drivers/xen/blkback/blkback.c b/drivers/xen/blkback/blkback.c
index 8d988f4..996869e 100644
--- a/drivers/xen/blkback/blkback.c
+++ b/drivers/xen/blkback/blkback.c
@@ -203,6 +203,14 @@ static void print_stats(blkif_t *blkif)
blkif->st_oo_req = 0;
}
+static void refill_reqcount(blkif_t *blkif)
+{
+ blkif->reqtime = jiffies + msecs_to_jiffies(1000);
+ blkif->reqcount += blkif->reqrate;
+ if (blkif->reqcount > blkif->reqmax)
+ blkif->reqcount = blkif->reqmax;
+}
+
int blkif_schedule(void *arg)
{
blkif_t *blkif = arg;
@@ -232,6 +240,9 @@ int blkif_schedule(void *arg)
if (log_stats && time_after(jiffies, blkif->st_print))
print_stats(blkif);
+
+ if (time_after(jiffies, blkif->reqtime))
+ refill_reqcount(blkif);
}
if (log_stats)
@@ -313,11 +324,22 @@ 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 tokens right now, and limiting
+ * is requested, then don't bother with going any further. */
+ if (blkif->reqcount <= 0 && blkif->reqmax != 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->reqcount <= 0) {
+ more_to_do = 1;
+ break;
+ }
+
if (kthread_should_stop()) {
more_to_do = 1;
break;
diff --git a/drivers/xen/blkback/common.h b/drivers/xen/blkback/common.h
index 57b7825..45af42f 100644
--- a/drivers/xen/blkback/common.h
+++ b/drivers/xen/blkback/common.h
@@ -92,6 +92,12 @@ typedef struct blkif_st {
grant_handle_t shmem_handle;
grant_ref_t shmem_ref;
+
+ /* qos information */
+ long reqtime;
+ int reqcount;
+ int reqmax;
+ int reqfill;
} blkif_t;
blkif_t *blkif_alloc(domid_t domid);
--
1.6.1.3
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