James Smart wrote: > > > Vasu Dev wrote: >> On Mon, 2009-10-19 at 11:32 -0700, Joe Eykholt wrote: >>> The FC-LS spec. says ELS timeouts should be 2 x R_A_TOV. >>> The FC-GS spec. says CT timeouts should be 3 x R_A_TOV. >>> >>> We've been using E_D_TOV for both of those. >>> >>> Change for all ELS and CT requests except FLOGI, which we >>> leave at 2 seconds (using E_D_TOV). One could argue that >>> R_A_TOV is locally determined until after FLOGI succeeds. >>> >>> This does change FLOGI for vports which becomes FDISC. >>> This does not change the REC/SRR timeout which is 2 seconds. >> >> The FCP sec 11 suggests REC timeout at least >= E_D_TOV + 1 seconds and >> default E_D_TOV as 2s, that means it should be least 3 second. > > A round trip time with 1 second to spare. Pretty tight if E_D_TOV is > accurate.
But E_D_TOV is very conservative. A round trip time is a few milliseconds. The REC_TOV specifies how often to send an REC while the I/O is outstanding, not how long to wait for the REC response. >> The FCP >> standard requires minimum value for REC_TOV and as far as I can tell >> there is no restriction on larger REC_TOV value, that means we could >> choose higher values > > True - but I look at FC-LS as giving the recommendation for any ELS. There are really two timeouts here, one is how long we wait for an I/O before sending a REC (REC_TOV) another is how long we wait for the reply to the REC. The latter should be 2 * R_A_TOV, according to FC-LS. A healthy target should reply right away, so a longer timeout won't hurt anything. REC_TOV should be E_D_TOV + 1s as Vasu points out. It would usually only come into play for tape recovery on long ops. Longer timeouts could lead to really long recovery times for dropped frames, and I think we want to do REC before SCSI times out. >> also and I think we should since FCoE is mostly >> used with 4G FC target ports and currently we allow upto 1024 commands >> with each cmd could be up to 512KB and I've seen some config having low >> IO throughout. So may be it should 20-30 seconds to avoid pre-mature REC >> attempts. > > Agreed - to be safe, moving to the 2*R_A_TOV FC-LS recommendation seems > a safe approach. > > -- james > >> >> I heard some HBA uses ULP_TOV (FC_SCSI_TM_TOV etc in libfc) as much as >> 60HZ, so perhaps that also need to be increased to avoid thrash due to >> too early timeout and retry attempts. >> >> What do you think ? >> >> Vasu >> >> >> _______________________________________________ >> devel mailing list >> [email protected] >> http://www.open-fcoe.org/mailman/listinfo/devel >> _______________________________________________ devel mailing list [email protected] http://www.open-fcoe.org/mailman/listinfo/devel
