If xcopy between two devices fails, it is pointless to send more xcopy
command between there two devices because they take time and they will
likely also fail.
This patch keeps a cache of (source_device,destination_device) pairs where
copying failed and makes sure that no xcopy command is sooner than 30
seconds after the last failure.
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
---
drivers/scsi/sd.c | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
Index: linux-4.4-rc4/drivers/scsi/sd.c
===================================================================
--- linux-4.4-rc4.orig/drivers/scsi/sd.c 2015-12-07 16:59:09.000000000
+0100
+++ linux-4.4-rc4/drivers/scsi/sd.c 2015-12-07 16:59:12.000000000 +0100
@@ -939,6 +939,26 @@ static void sd_config_copy(struct scsi_d
(logical_block_size >> 9));
}
+#define SD_COPY_DISABLED_CACHE_TIME (HZ * 30)
+#define SD_COPY_DISABLED_CACHE_HASH_BITS 6
+#define SD_COPY_DISABLED_CACHE_HASH (1 <<
SD_COPY_DISABLED_CACHE_HASH_BITS)
+
+struct sd_copy_disabled_cache_entry {
+ struct scsi_device *src;
+ struct scsi_device *dst;
+ unsigned long jiffies;
+};
+
+static struct sd_copy_disabled_cache_entry
sd_copy_disabled_cache[SD_COPY_DISABLED_CACHE_HASH];
+
+static struct sd_copy_disabled_cache_entry *sd_copy_disabled_cache_hash(
+ struct scsi_device *src, struct scsi_device *dst)
+{
+ return &sd_copy_disabled_cache[
+ hash_long((unsigned long)src + ((unsigned long)dst >> 1),
SD_COPY_DISABLED_CACHE_HASH_BITS)
+ ];
+}
+
static int sd_setup_copy_cmnd(struct scsi_cmnd *cmd)
{
struct request *rq = cmd->request;
@@ -951,6 +971,7 @@ static int sd_setup_copy_cmnd(struct scs
struct bio *bio = rq->bio;
struct page *page;
unsigned char *buf;
+ struct sd_copy_disabled_cache_entry *e;
dst_sdp = scsi_disk(rq->rq_disk)->device;
dst_queue = rq->rq_disk->queue;
@@ -970,6 +991,12 @@ static int sd_setup_copy_cmnd(struct scs
if (src_sdp->sector_size != dst_sdp->sector_size)
return BLKPREP_KILL;
+ /* The copy failed in the past, so do not retry it for some time */
+ e = sd_copy_disabled_cache_hash(src_sdp, dst_sdp);
+ if (unlikely(jiffies - ACCESS_ONCE(e->jiffies) <
SD_COPY_DISABLED_CACHE_TIME) &&
+ likely(ACCESS_ONCE(e->src) == src_sdp) &&
likely(ACCESS_ONCE(e->dst) == dst_sdp))
+ return BLKPREP_KILL;
+
dst_lba = blk_rq_pos(rq) >> (ilog2(dst_sdp->sector_size) - 9);
src_lba = bio->bi_copy->pair[0]->bi_iter.bi_sector >>
(ilog2(src_sdp->sector_size) - 9);
nr_blocks = blk_rq_sectors(rq) >> (ilog2(dst_sdp->sector_size) - 9);
@@ -2003,6 +2030,16 @@ static int sd_done(struct scsi_cmnd *SCp
*/
case EXTENDED_COPY:
if ((SCpnt->cmnd[1] & 0x1f) == 0) {
+ struct sd_copy_disabled_cache_entry *e;
+ struct scsi_device *src_sdp, *dst_sdp;
+
+ dst_sdp = sdkp->device;
+ src_sdp =
scsi_disk(req->bio->bi_copy->pair[0]->bi_bdev->bd_disk)->device;
+ e =
sd_copy_disabled_cache_hash(src_sdp, dst_sdp);
+ ACCESS_ONCE(e->src) = src_sdp;
+ ACCESS_ONCE(e->dst) = dst_sdp;
+ ACCESS_ONCE(e->jiffies) = jiffies;
+
good_bytes = 0;
req->__data_len = blk_rq_bytes(req);
req->cmd_flags |= REQ_QUIET;
--
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