From 8550170477df37365718dd617b67f69e0956161c Mon Sep 17 00:00:00 2001 From: Warner Losh Date: Thu, 8 Jan 2009 00:45:47 +0000 Subject: [PATCH] Make it possible to override the number of retries for the CD media. When trying to read scratched or damaged CDs and DVDs, the default mechanism is sub-optimal. Programs like ddrescue do much better if you turn off retries entirely, since their algorithms are designed scan big areas fast, then winnow the areas down. Turning off retries speeds these programs up by as much as 20x, since the drive is able to 'stream past' many small errors... The sysctl/tunable kern.cam.cd.retry_count controls this. That defaults to '4' (for a total of 5 attempts). Setting to 0 turns off all retry attempts. Reviewed by: scottl@ --- sys/cam/scsi/scsi_cd.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/sys/cam/scsi/scsi_cd.c b/sys/cam/scsi/scsi_cd.c index 383d70319848..8eb353753aa8 100644 --- a/sys/cam/scsi/scsi_cd.c +++ b/sys/cam/scsi/scsi_cd.c @@ -292,6 +292,9 @@ static struct periph_driver cddriver = 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 @@ PERIPHDRIVER_DECLARE(cd, cddriver); #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 @@ cdstart(struct cam_periph *periph, union ccb *start_ccb) 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,