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Re: sector alignment for DataOut PDUs?
The sender should definitely avoid sending less data than the negotiated value of unsolicited data length when more data is available to be sent. However, the total data length available to be sent itself could be lesser than the negotiated value. This suggests that while we should mandate the receiver to accept anything less than the negotiated value, we should not force the initiator to send exactly the same value as the negotiated value. In other words, we cannot "forbid the sender sending less than the negotiated value". I'm for the first option suggested by Paul. BTW, can we change "data amount" to "size of data" to be sent ? Regards, Sajay Paul Koning wrote: > > >>>>> "Julian" == Julian Satran <Julian_Satran@il.ibm.com> writes: > > Julian> Where is the hint you are alluding to? > > >> .... (It does > >> hint that targets may object if you don't do it that way -- > >> which makes no sense at all unless there's a MUST for > >> initiators to do what targets are allowed to expect.) > > In this section: > > 9.5 Unsolicited Data and Performance > > Unsolicited data on write are meant to reduce the effect > of latency on throughput (no R2T is needed to start send- > ing data). In addition, immediate data are meant to > reduce the protocol overhead (both bandwidth and execu- > tion time). > > However, negotiating an amount of unsolicited data for > writes and sending less than the negotiated amount when > the total data amount to be sent by a command is larger > than the negotiated amount may negatively impact perfor- > mance and may not be supported by all the targets. > > Specifically, the last sentence. That statement is not a good thing, > because it explicitly permits failures to interoperate, which a > protocol standard must never do. Instead, a receiver must always be > required to accept anything that the standard permits the sender to > send in a state that the sender can legitimately get to. > > There are two ways to fix this: one is to forbid the sender sending > less than the negotiated unsolicited data length. The other is to > require the receiver to accept unsolicited data of less than the > negotiated length. Either change works because either change > establishes interoperability. > > paul -- http://san.hcltech.com
Last updated: Thu Feb 28 12:18:07 2002
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