Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 08/13] IB/iser: set virt_boundary_mask in the scsi host
To:     Jason Gunthorpe <jgg@ziepe.ca>, Christoph Hellwig <hch@lst.de>
Cc:     Jens Axboe <axboe@kernel.dk>, Sebastian Ott <sebott@linux.ibm.com>,
        Max Gurtovoy <maxg@mellanox.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Oliver Neukum <oneukum@suse.com>, linux-block@vger.kernel.org,
        linux-rdma@vger.kernel.org, linux-mmc@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org,
        megaraidlinux.pdl@broadcom.com, MPT-FusionLinux.pdl@broadcom.com,
        linux-hyperv@vger.kernel.org, linux-usb@vger.kernel.org,
        usb-storage@lists.one-eyed-alien.net, linux-kernel@vger.kernel.org
References: <20190605190836.32354-1-hch@lst.de>
 <20190605190836.32354-9-hch@lst.de> <20190605202235.GC3273@ziepe.ca>
From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <b3e46295-4257-86ad-6994-f83b736c8f40@grimberg.me>
Date:   Wed, 5 Jun 2019 16:35:12 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.6.1
MIME-Version: 1.0
In-Reply-To: <20190605202235.GC3273@ziepe.ca>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


>> This ensures all proper DMA layer handling is taken care of by the
>> SCSI midlayer.
> 
> Maybe not entirely related to this series, but it looks like the SCSI
> layer is changing the device global dma_set_max_seg_size() - at least
> in RDMA the dma device is being shared between many users, so we
> really don't want SCSI to make this value smaller.
> 
> Can we do something about this?

srp seems to do the right thing:
target_host->max_segment_size = ib_dma_max_seg_size(ibdev);

But iser does not, which means that scsi limits it to:
BLK_MAX_SEGMENT_SIZE (64k)

I can send a fix to iser.

> Wondering about other values too, and the interaction with the new
> combining stuff in umem.c

The only other values AFAICT is the dma_boundary that rdma llds don't
set...