On 08/26/2013 08:27 PM, Mike Dawson wrote:
Josh,
The original bug is marked as krbd, but could this bug could affect rbd
volumes mounted via qemu as well? If so, could you describe how it might
block a qemu guest?
No, this is just a patch for the kernel rbd driver, which doesn't
affect qemu at all.
We've been fighting i/o issues on some of our guests for some time. With
qemu 1.4.0, we saw the entire guest freeze. But now with qemu 1.5.2
which includes your asynchronous flush patch, the issue is typified by
periodic dips in performance and high latency (especially for reads, it
seems). Could this bug be related?
A good next step for tracking this down would be narrowing in on the
source of the periods of high latency - starting with whether they're
primarily coming from the server or client side. Since it's especially
reads, I'd guess it's more likely to be an osd-side issue. If you look
at the admin socket's dump_historic_ops do you see higher op durations
around the dips in performance? What about any correlation with
underlying disk stats from iostat -x?
Thanks,
Mike Dawson
On 8/26/2013 9:34 PM, Josh Durgin wrote:
When a request returns an error, the driver needs to report the entire
extent of the request as completed. Writes already did this, since
they always set xferred = length, but reads were skipping that step if
an error other than -ENOENT occurred. Instead, rbd would end up
passing 0 xferred to blk_end_request(), which would always report
needing more data. This resulted in an assert failing when more data
was required by the block layer, but all the object requests were
done:
[ 1868.719077] rbd: obj_request read result -108 xferred 0
[ 1868.719077]
[ 1868.719518] end_request: I/O error, dev rbd1, sector 0
[ 1868.719739]
[ 1868.719739] Assertion failure in rbd_img_obj_callback() at line 1736:
[ 1868.719739]
[ 1868.719739] rbd_assert(more ^ (which ==
img_request->obj_request_count));
Without this assert, reads that hit errors would hang forever, since
the block layer considered them incomplete.
Fixes: http://tracker.ceph.com/issues/5647
Signed-off-by: Josh Durgin <josh.durgin@xxxxxxxxxxx>
---
drivers/block/rbd.c | 14 +++++++-------
1 files changed, 7 insertions(+), 7 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 0d669ae..f8fd7d3 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1557,11 +1557,12 @@ rbd_img_obj_request_read_callback(struct
rbd_obj_request *obj_request)
obj_request, obj_request->img_request, obj_request->result,
xferred, length);
/*
- * ENOENT means a hole in the image. We zero-fill the
- * entire length of the request. A short read also implies
- * zero-fill to the end of the request. Either way we
- * update the xferred count to indicate the whole request
- * was satisfied.
+ * ENOENT means a hole in the image. We zero-fill the entire
+ * length of the request. A short read also implies zero-fill
+ * to the end of the request. An error requires the whole
+ * length of the request to be reported finished with an error
+ * to the block layer. In each case we update the xferred
+ * count to indicate the whole request was satisfied.
*/
rbd_assert(obj_request->type != OBJ_REQUEST_NODATA);
if (obj_request->result == -ENOENT) {
@@ -1570,14 +1571,13 @@ rbd_img_obj_request_read_callback(struct
rbd_obj_request *obj_request)
else
zero_pages(obj_request->pages, 0, length);
obj_request->result = 0;
- obj_request->xferred = length;
} else if (xferred < length && !obj_request->result) {
if (obj_request->type == OBJ_REQUEST_BIO)
zero_bio_chain(obj_request->bio_list, xferred);
else
zero_pages(obj_request->pages, xferred, length);
- obj_request->xferred = length;
}
+ obj_request->xferred = length;
obj_request_done_set(obj_request);
}
--
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