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From: Christoph Hellwig <hch@lst.de>
To: 鑫愿 <qiuxincsu@sina.com>
Cc: Bart Van Assche <bart.vanassche@sandisk.com>,
	Jens Axboe <axboe@fb.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	James Bottomley <jejb@linux.vnet.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Mike Snitzer <snitzer@redhat.com>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	Ming Lei <tom.leiming@gmail.com>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	Keith Busch <keith.busch@intel.com>,
	Doug Ledford <dledford@redhat.com>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	Laurence Oberman <loberman@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	"tiger.zhao" <tiger.zhao@huawei.com>, qiuxin <qiuxin@huawei.com>
Subject: Re: A question regarding "multiple SGL"
Date: Thu, 27 Oct 2016 08:41:15 +0200	[thread overview]
Message-ID: <20161027064115.GA5864@lst.de> (raw)
In-Reply-To: <20161027005230.9904DC00097@webmail.sinamail.sina.com.cn>

Hi Robert,

There is no feature called "Multiple SGL in one NVMe capsule".  The
NVMe over Fabrics specification allows a controller to advertise how
many SGL descriptors it supports using the MSDBD Identify field:

"Maximum SGL Data Block Descriptors (MSDBD): This field indicates the
maximum number of (Keyed) SGL Data Block descriptors that a host is allowed to
place in a capsule. A value of 0h indicates no limit."

Setting this value to 1 is perfectly valid.  Similarly a host is free
to chose any number of SGL descriptors between 0 (only for command that
don't transfer data) to the limit imposed by the controller using the
MSDBD field.

There are no plans to support a MSDBD value larger than 1 in the Linux
NVMe target, and there are no plans to ever submit commands with multiple
SGLs from the host driver either.

Cheers,
	Christoph

WARNING: multiple messages have this Message-ID (diff)
From: hch@lst.de (Christoph Hellwig)
Subject: A question regarding "multiple SGL"
Date: Thu, 27 Oct 2016 08:41:15 +0200	[thread overview]
Message-ID: <20161027064115.GA5864@lst.de> (raw)
In-Reply-To: <20161027005230.9904DC00097@webmail.sinamail.sina.com.cn>

Hi Robert,

There is no feature called "Multiple SGL in one NVMe capsule".  The
NVMe over Fabrics specification allows a controller to advertise how
many SGL descriptors it supports using the MSDBD Identify field:

"Maximum SGL Data Block Descriptors (MSDBD): This field indicates the
maximum number of (Keyed) SGL Data Block descriptors that a host is allowed to
place in a capsule. A value of 0h indicates no limit."

Setting this value to 1 is perfectly valid.  Similarly a host is free
to chose any number of SGL descriptors between 0 (only for command that
don't transfer data) to the limit imposed by the controller using the
MSDBD field.

There are no plans to support a MSDBD value larger than 1 in the Linux
NVMe target, and there are no plans to ever submit commands with multiple
SGLs from the host driver either.

Cheers,
	Christoph

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
To: 鑫愿 <qiuxincsu-k+cT0dCbe1g@public.gmane.org>
Cc: Bart Van Assche
	<bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>,
	Jens Axboe <axboe-b10kYP2dOMg@public.gmane.org>,
	"linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	James Bottomley
	<jejb-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
	"Martin K. Petersen"
	<martin.petersen-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>,
	Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Ming Lei <tom.leiming-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	"linux-nvme-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
	<linux-nvme-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>,
	Keith Busch <keith.busch-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Laurence Oberman
	<loberman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>,
	"tiger.zhao" <tiger.zhao-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>,
	qiuxin <qiuxin-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Subject: Re: A question regarding "multiple SGL"
Date: Thu, 27 Oct 2016 08:41:15 +0200	[thread overview]
Message-ID: <20161027064115.GA5864@lst.de> (raw)
In-Reply-To: <20161027005230.9904DC00097-2RFepEojUI2gQzYKMK1YzK/p1tWXv8elb9TvmfFkwKk@public.gmane.org>

Hi Robert,

There is no feature called "Multiple SGL in one NVMe capsule".  The
NVMe over Fabrics specification allows a controller to advertise how
many SGL descriptors it supports using the MSDBD Identify field:

"Maximum SGL Data Block Descriptors (MSDBD): This field indicates the
maximum number of (Keyed) SGL Data Block descriptors that a host is allowed to
place in a capsule. A value of 0h indicates no limit."

Setting this value to 1 is perfectly valid.  Similarly a host is free
to chose any number of SGL descriptors between 0 (only for command that
don't transfer data) to the limit imposed by the controller using the
MSDBD field.

There are no plans to support a MSDBD value larger than 1 in the Linux
NVMe target, and there are no plans to ever submit commands with multiple
SGLs from the host driver either.

Cheers,
	Christoph
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       reply	other threads:[~2016-10-27  6:41 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20161027005230.9904DC00097@webmail.sinamail.sina.com.cn>
2016-10-27  6:41 ` Christoph Hellwig [this message]
2016-10-27  6:41   ` A question regarding "multiple SGL" Christoph Hellwig
2016-10-27  6:41   ` Christoph Hellwig
2016-10-27  6:57   ` Qiuxin (robert)
2016-10-27  6:57     ` Qiuxin (robert)
2016-10-27  6:57     ` Qiuxin (robert)
2016-10-27  7:10     ` Christoph Hellwig
2016-10-27  7:10       ` Christoph Hellwig
2016-10-27  9:02       ` Sagi Grimberg
2016-10-27  9:02         ` Sagi Grimberg
2016-10-27  9:02         ` Sagi Grimberg
2016-10-27 14:50         ` Steve Wise
2016-10-27 14:50           ` Steve Wise
2016-10-27 14:50           ` Steve Wise

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