linux-kernel - Re: [RFC-v3 9/9] iser-target: Add iSCSI Extensions for RDMA (iSER) target driver

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Date:	Thu, 04 Apr 2013 15:17:27 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Or Gerlitz <ogerlitz@...lanox.com>
Cc:	target-devel <target-devel@...r.kernel.org>,
	linux-rdma <linux-rdma@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Roland Dreier <roland@...nel.org>,
	Alexander Nezhinsky <alexandern@...lanox.com>
Subject: Re: [RFC-v3 9/9] iser-target: Add iSCSI Extensions for RDMA (iSER)
 target driver

On Thu, 2013-04-04 at 12:45 +0300, Or Gerlitz wrote:
> On 04/04/2013 10:24, Nicholas A. Bellinger wrote:
> 
> > +#define ISER_RECV_DATA_SEG_LEN  8192
> > +#define ISER_RX_PAYLOAD_SIZE    (ISER_HEADERS_LEN + ISER_RECV_DATA_SEG_LEN)
> > [...]
> > +#define ISER_RX_PAD_SIZE	(16384 - (ISER_RX_PAYLOAD_SIZE + \
> > +					sizeof(u64) + sizeof(struct ib_sge)))
> 
> We're eating here too much ram for the pad, you need 8K + something, so 
> the pad can count down
> from 12K and not 16K which means each such element will consume three 
> pages and not four.
> 

Hmm, IIRC this larger pad was originally required after bumping the
ISER_RECV_DATA_SEG_LEN value for handling incoming ImmediateData and
Unsolicited Data-OUT..  Will try using 12k here and see what happens..

Also, ISER_RECV_DATA_SEG_LEN will need to be enforced as the largest
MaxRecvDataSegmentLength negotiated during iser login to prevent the
initiator from exceeding the hardcoded value..

> > +struct iser_rx_desc {
> > +	struct iser_hdr iser_header;
> > +	struct iscsi_hdr iscsi_header;
> > +	char		data[ISER_RECV_DATA_SEG_LEN];
> > +	u64		dma_addr;
> > +	struct ib_sge	rx_sg;
> > +	char		pad[ISER_RX_PAD_SIZE];
> > +} __packed;
> > +
> > +struct isert_rx_desc {
> > +	struct isert_conn	*desc_conn;
> > +	struct work_struct	desc_work;
> > +	struct iser_rx_desc	desc;
> > +} __packed;
> 
> You have way enough room in the pad field of struct iser_rx_desc to 
> place there the two fields
> added by struct isert_rx_desc (and you only use struct iser_rx_desc from 
> within isert_rx_desc) --> any reason
> not to unify  them?
> 

This is left-over cruft from the per isert_rx_desc dispatch into process
context..  Dropping this now.

--nab

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