RE: [PATCH 3/3 V2] alua: backoff alua rtpg retry linearly vs. geometrically

["Moger, Babu" <Babu.Moger@xxxxxxxxxx>]

> -----Original Message-----
> From: linux-scsi-owner@xxxxxxxxxxxxxxx [mailto:linux-scsi-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Rob Evers
> Sent: Friday, May 18, 2012 1:09 PM
> To: linux-scsi@xxxxxxxxxxxxxxx
> Subject: [PATCH 3/3 V2] alua: backoff alua rtpg retry linearly vs. geometrically
> 
> Currently the backoff algorithm for when to retry alua rtpg
> requests progresses geometrically as so:
> 
> 2, 4, 8, 16, 32, 64... seconds.
> 
> This progression can lead to un-needed delay in retrying
> alua rtpg requests when the rtpgs are delayed.  A less
> aggressive backoff algorithm that is additive would not
> lead to such large jumps when delays start getting long, but
> would backoff linearly:
> 
> 2, 4, 6, 8, 10... seconds.
> 
> Signed-off-by: Martin George <marting@xxxxxxxxxx>
> Signed-off-by: Rob Evers <revers@xxxxxxxxxx>

Reviewed-by: Babu Moger <babu.moger@xxxxxxxxxx>

> ---
>  drivers/scsi/device_handler/scsi_dh_alua.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c
> b/drivers/scsi/device_handler/scsi_dh_alua.c
> index 51d8cf6..7eb9dea 100644
> --- a/drivers/scsi/device_handler/scsi_dh_alua.c
> +++ b/drivers/scsi/device_handler/scsi_dh_alua.c
> @@ -522,7 +522,7 @@ static int alua_rtpg(struct scsi_device *sdev, struct
> alua_dh_data *h)
>  	unsigned char *ucp;
>  	unsigned err;
>  	bool rtpg_ext_hdr_req = 1;
> -	unsigned long expiry, interval = 1000;
> +	unsigned long expiry, interval = 0;
>  	unsigned int tpg_desc_tbl_off;
>  	unsigned char orig_transition_tmo;
> 
> @@ -625,7 +625,7 @@ static int alua_rtpg(struct scsi_device *sdev, struct
> alua_dh_data *h)
>  	case TPGS_STATE_TRANSITIONING:
>  		if (time_before(jiffies, expiry)) {
>  			/* State transition, retry */
> -			interval *= 2;
> +			interval += 2000;
>  			msleep(interval);
>  			goto retry;
>  		}
> --
> 1.7.7.2
> 
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