Date: Tue, 06 Jan 2009 20:37:36 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: scsi@FreeBSD.org Subject: Patch review Message-ID: <20090106.203736.-1300543249.imp@bsdimp.com>
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What do people think of this? It is very useful when trying to
recover a CD/DVD that's been scratched with ddrescue which handles all
the retry logic. This patch is modeled after the
kern.cam.da.retry_count sysctl and friends.
This makes ddrescue about between 5x and 20x faster. The reason for
the large delta is that it can now 'stream' past errors rather than
doing a lot of reseeking when reading a large block size. I've also
observed fewer hangs in one of the cheap DVD drives I tried this with,
likely due to fewer forced retries frying its brain... Of course, all
of this was with kern.cam.cd.retry_count = 0. I've not changed the
default behavior.
Comments?
Warner
P.S. I have a recollection that Scott Long sent me something akin to
this, but I couldn't find it so I just recreated this trivial patch
from scratch, cheating off of scsi_da.c.
Index: cam/scsi/scsi_cd.c
===================================================================
--- cam/scsi/scsi_cd.c (revision 186807)
+++ cam/scsi/scsi_cd.c (working copy)
@@ -292,6 +292,9 @@
PERIPHDRIVER_DECLARE(cd, cddriver);
+#ifndef CD_DEFAULT_RETRY
+#define CD_DEFAULT_RETRY 4
+#endif
#ifndef CHANGER_MIN_BUSY_SECONDS
#define CHANGER_MIN_BUSY_SECONDS 5
#endif
@@ -299,11 +302,15 @@
#define CHANGER_MAX_BUSY_SECONDS 15
#endif
+static int cd_retry_count = CD_DEFAULT_RETRY;
static int changer_min_busy_seconds = CHANGER_MIN_BUSY_SECONDS;
static int changer_max_busy_seconds = CHANGER_MAX_BUSY_SECONDS;
SYSCTL_NODE(_kern_cam, OID_AUTO, cd, CTLFLAG_RD, 0, "CAM CDROM driver");
SYSCTL_NODE(_kern_cam_cd, OID_AUTO, changer, CTLFLAG_RD, 0, "CD Changer");
+SYSCTL_INT(_kern_cam_cd, OID_AUTO, retry_count, CTLFLAG_RW,
+ &cd_retry_count, 0, "Normal I/O retry count");
+TUNABLE_INT("kern.cam.cd.retry_count", &cd_retry_count);
SYSCTL_INT(_kern_cam_cd_changer, OID_AUTO, min_busy_seconds, CTLFLAG_RW,
&changer_min_busy_seconds, 0, "Minimum changer scheduling quantum");
TUNABLE_INT("kern.cam.cd.changer.min_busy_seconds", &changer_min_busy_seconds);
@@ -1454,7 +1461,7 @@
devstat_start_transaction_bio(softc->disk->d_devstat, bp);
scsi_read_write(&start_ccb->csio,
- /*retries*/4,
+ /*retries*/cd_retry_count,
/* cbfcnp */ cddone,
MSG_SIMPLE_Q_TAG,
/* read */bp->bio_cmd == BIO_READ,
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