On Fri, 19 Jun 2009 11:52:00 +0200 Arne Redlich <arne.redlich@xxxxxxxxxxxxxx> wrote: > Am Freitag, den 19.06.2009, 17:44 +0900 schrieb FUJITA Tomonori: > > On Fri, 19 Jun 2009 10:37:49 +0200 > > Arne Redlich <arne.redlich@xxxxxxxxxxxxxx> wrote: > > > > > Am Freitag, den 19.06.2009, 16:54 +0900 schrieb FUJITA Tomonori: > > > > On Wed, 17 Jun 2009 08:46:50 +0200 > > > > Arne Redlich <arne.redlich@xxxxxxxxxxxxxx> wrote: > > > > > > > > This wasn't an interpretation as the specs leave absolutely no room for > > > > > that, I was just rephrasing them. Here's the verbatim quotes: > > > > > > > > > > RFC 3720 (iSCSI), 10.8.4 (Desired Data Transfer Length and Buffer > > > > > Offset): > > > > > "The Desired Data Transfer Length MUST NOT be 0 and MUST not exceed > > > > > MaxBurstLength." > > > > > > > > > > RFC 5046 (iSER), 7.3.6 (Ready To Transfer (R2T)): > > > > > "4. [..] To transform the R2T PDU, the iSER layer at the target: [...] > > > > > d. MUST use the Desired Data Transfer Length from the R2T PDU as the > > > > > RDMA Read Message Size of the RDMA Read Request Message." > > > > > > > > In iSER case, the Desired Data Transfer Length MUST not exceed WHAT? > > > > > > MaxBurstLength (or the limit incurred by the implementation, i.e. the > > > iSER mempool, depends on which is smaller). > > > > Thanks, > > > > Can you tell me where I can find the description about it in RFC 5046? > > > > And can you also tell me where I can find the description about the > > length limitation of Data-in in RFC 5046 (your patch uses the max > > burst in iSER)? > > See above for the section info. It's a consequence of _both_ specs: Ah, I didn't know that both specs define ISER. > an R2T must not request more than MaxBurstLength bytes, and since an R2T > is transformed into an RDMA read, the RDMA read must not request more > than MaxBurstLength bytes. > > For Data-In. That's ia bit less clear. Here's the reasoning that lead me > to version in the patch. > > RFC 3720, 12.13 (MaxBurstLength): > "The initiator and target negotiate maximum SCSI data payload in bytes > in a Data-In or a solicited Data-Out iSCSI sequence. A sequence > consists of one or more consecutive Data-In or Data-Out PDUs that end > with a Data-In or Data-Out PDU with the F bit set to one". > > Data-Ins are translated to RDMA Writes and iSER obsoletes MaxRecvDSL, > it's replaced with Initiator- / TargetRecvDSL but only for _control_ > type PDUs: > > RFC 5046, 6.2 (MaxRecvDataSegmentLength): > "[...] Similarly, the target MUST consider the value of its local > MaxRecvDataSegmentLength (that it would have declared to the initiator) > as having the value of TargetRecvDataSegmentLength, and the value of the > remote MaxRecvDataSegmentLength (that would have been declared by the > initiator) as having the value of InitiatorRecvDataSegmentLength. > > The MaxRecvDataSegmentLength key is applicable only for iSCSI > control-type PDUs." > > RFC 5046, 7.3.5 (SCSI Data-In): > "2. It MUST generate and send an RDMA Write Message containing the read > data to the initiator [...] > c. It MUST use DataSegmentLength from the SCSI Data-in PDU to determine > the amount of data to be sent in the RDMA Write Message." OK, then I guess that iSER wants limit MaxBusrtLength to RDMA_TRANSFER_SIZE to avoid breakage and set the default MaxBusrtLength value to RDMA_TRANSFER_SIZE to avoid the performance drop (with initiators that are not configured with large MaxBusrtLength values). Right? Thanks, -- To unsubscribe from this list: send the line "unsubscribe stgt" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
