From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Kalderon, Michal" <Michal.Kalderon@cavium.com>
Subject: Re: SQ overflow seen running isert traffic with high block sizes
Date: Fri, 19 Jan 2018 19:33:22 +0000
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To: "Nicholas A. Bellinger" <nab@linux-iscsi.org>, Shiraz Saleem <shiraz.saleem@intel.com>
Cc: "Amrani, Ram" <Ram.Amrani@cavium.com>, Sagi Grimberg <sagi@grimberg.me>, "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>, "Elior, Ariel" <Ariel.Elior@cavium.com>, target-devel <target-devel@vger.kernel.org>, Potnuri Bharat Teja <bharat@chelsio.com>, "Radzi, Amit" <Amit.Radzi@cavium.com>, "Galon, Yoav" <Yoav.Galon@cavium.com>
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________________________________________
From: Nicholas A. Bellinger <nab@linux-iscsi.org>
Sent: Thursday, January 18, 2018 11:58 AM

> Hi Shiraz, Michal & Co,
Hi Nicholas,=20

> Thanks for the feedback.  Comments below.

> A couple of thoughts.

> First, would it be helpful to limit maximum payload size per I/O for
> consumers based on number of iser-target sq hw sges..?

I don't think you need to limit the maximum payload, but instead=20
initialize the max_wr to be based on the number of supported SGEs
Instead of what is there today:
#define ISERT_QP_MAX_REQ_DTOS   (ISCSI_DEF_XMIT_CMDS_MAX +    \
                                ISERT_MAX_TX_MISC_PDUS  + \
                                ISERT_MAX_RX_MISC_PDUS)
Add the maximum number of WQEs per command,=20
The calculation of number of WQEs per command needs to be something like
"MAX_TRANSFER_SIZE/(numSges*PAGE_SIZE)".

For some devices like ours, breaking the IO into multiple WRs according to =
supported
number of SGEs doesn't necessarily means performance penalty.

thanks,
Michal