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From: Sagi Grimberg <sagi-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
To: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
Cc: Max Gurtovoy <maxg-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>,
	linux-nvme-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	keith.busch-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org,
	linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
	vladimirk-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org
Subject: Re: [PATCH v2 3/4] nvme: enable SG gaps support
Date: Sun, 23 Apr 2017 12:45:39 +0300	[thread overview]
Message-ID: <9fe3f5fa-4496-3819-0288-08a073dd1a1a@grimberg.me> (raw)
In-Reply-To: <20170423084553.GA24434-jcswGhMUV9g@public.gmane.org>


> Each block queue has a ->dma_alignment field, which is set to 511
> by default unless changed.  Everything not aligned to that will be
> bounced in __blk_rq_map_user_iov and friends before we send it to
> the driver.

Thanks, I missed the default setting...

>> I also just tested Bart's unaligned test [1] on scsi_debug and it seems
>> to go through as well (alignment and length are 4)...
>
> SCSI reduces the alignment in __scsi_init_queue:
>
> 	/*
>          * set a reasonable default alignment on word boundaries: the
> 	 * host and device may alter it using
> 	 * blk_queue_update_dma_alignment() later.
> 	 */
> 	blk_queue_dma_alignment(q, 0x03);

That explains why I was able to test that with iSER :)

I guess I didn't test single byte alignment after all, but
I definitely remember using less than a sector...

> still would fit NVMe dword-alignment SGLs, though :)

I would say its useful to have, but its only relevant to ioctls as
normal io we explicitly on sub logical block size alignment.

Anyways, I still think having ctrl->virt_boundary instead of
ctrl->sg_gap_support is cleaner...
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WARNING: multiple messages have this Message-ID (diff)
From: sagi@grimberg.me (Sagi Grimberg)
Subject: [PATCH v2 3/4] nvme: enable SG gaps support
Date: Sun, 23 Apr 2017 12:45:39 +0300	[thread overview]
Message-ID: <9fe3f5fa-4496-3819-0288-08a073dd1a1a@grimberg.me> (raw)
In-Reply-To: <20170423084553.GA24434@lst.de>


> Each block queue has a ->dma_alignment field, which is set to 511
> by default unless changed.  Everything not aligned to that will be
> bounced in __blk_rq_map_user_iov and friends before we send it to
> the driver.

Thanks, I missed the default setting...

>> I also just tested Bart's unaligned test [1] on scsi_debug and it seems
>> to go through as well (alignment and length are 4)...
>
> SCSI reduces the alignment in __scsi_init_queue:
>
> 	/*
>          * set a reasonable default alignment on word boundaries: the
> 	 * host and device may alter it using
> 	 * blk_queue_update_dma_alignment() later.
> 	 */
> 	blk_queue_dma_alignment(q, 0x03);

That explains why I was able to test that with iSER :)

I guess I didn't test single byte alignment after all, but
I definitely remember using less than a sector...

> still would fit NVMe dword-alignment SGLs, though :)

I would say its useful to have, but its only relevant to ioctls as
normal io we explicitly on sub logical block size alignment.

Anyways, I still think having ctrl->virt_boundary instead of
ctrl->sg_gap_support is cleaner...

  parent reply	other threads:[~2017-04-23  9:45 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-13 15:56 [PATCH v2 0/4] arbitrary sg lists support Max Gurtovoy
2017-04-13 15:56 ` Max Gurtovoy
     [not found] ` <1492098977-5231-1-git-send-email-maxg-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-04-13 15:56   ` [PATCH v2 1/4] IB/core: Add inline function to get sg mr type Max Gurtovoy
2017-04-13 15:56     ` Max Gurtovoy
     [not found]     ` <1492098977-5231-2-git-send-email-maxg-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-04-20 11:24       ` Sagi Grimberg
2017-04-20 11:24         ` Sagi Grimberg
2017-04-13 15:56   ` [PATCH v2 2/4] IB/iser: Use ib_get_sg_mr_type() helper Max Gurtovoy
2017-04-13 15:56     ` Max Gurtovoy
2017-04-13 15:56   ` [PATCH v2 3/4] nvme: enable SG gaps support Max Gurtovoy
2017-04-13 15:56     ` Max Gurtovoy
     [not found]     ` <1492098977-5231-4-git-send-email-maxg-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-04-20 11:27       ` Sagi Grimberg
2017-04-20 11:27         ` Sagi Grimberg
     [not found]         ` <2bd673ee-8455-32b7-1bad-34fa9eebb076-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
2017-04-21  6:44           ` Christoph Hellwig
2017-04-21  6:44             ` Christoph Hellwig
     [not found]             ` <20170421064427.GB6095-jcswGhMUV9g@public.gmane.org>
2017-04-23  7:20               ` Sagi Grimberg
2017-04-23  7:20                 ` Sagi Grimberg
     [not found]                 ` <9ff1a2e8-f84f-c772-e294-2339eee8e37d-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
2017-04-23  8:45                   ` Christoph Hellwig
2017-04-23  8:45                     ` Christoph Hellwig
     [not found]                     ` <20170423084553.GA24434-jcswGhMUV9g@public.gmane.org>
2017-04-23  9:45                       ` Sagi Grimberg [this message]
2017-04-23  9:45                         ` Sagi Grimberg
     [not found]                         ` <9fe3f5fa-4496-3819-0288-08a073dd1a1a-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
2017-04-23 13:23                           ` Max Gurtovoy
2017-04-23 13:23                             ` Max Gurtovoy
2017-04-24  7:02                           ` Christoph Hellwig
2017-04-24  7:02                             ` Christoph Hellwig
2017-04-13 15:56   ` [PATCH v2 4/4] nvme-rdma: add support for arbitrary sg lists mapping Max Gurtovoy
2017-04-13 15:56     ` Max Gurtovoy
2017-04-13 16:31   ` [PATCH v2 0/4] arbitrary sg lists support Bart Van Assche
2017-04-13 16:31     ` Bart Van Assche
     [not found]     ` <1492101079.5176.9.camel-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>
2017-04-13 16:46       ` Max Gurtovoy
2017-04-13 16:46         ` Max Gurtovoy
     [not found]         ` <9a8bc957-dcc0-2e54-d631-9f05f96e0f18-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-04-13 16:59           ` Laurence Oberman
2017-04-13 16:59             ` Laurence Oberman
2017-04-20 11:30       ` Sagi Grimberg
2017-04-20 11:30         ` Sagi Grimberg
     [not found]         ` <c52b5ce7-5346-419d-26f2-0d4d45d20471-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
2017-04-23 10:34           ` Leon Romanovsky
2017-04-23 10:34             ` Leon Romanovsky
     [not found]             ` <20170423103439.GC14088-U/DQcQFIOTAAJjI8aNfphQ@public.gmane.org>
2017-04-23 11:49               ` Sagi Grimberg
2017-04-23 11:49                 ` Sagi Grimberg
     [not found]                 ` <d697d360-99ca-c3ed-08e2-b89cc50a15b0-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
2017-04-23 12:12                   ` Leon Romanovsky
2017-04-23 12:12                     ` Leon Romanovsky
     [not found]                     ` <20170423121254.GD14088-U/DQcQFIOTAAJjI8aNfphQ@public.gmane.org>
2017-04-23 12:28                       ` Sagi Grimberg
2017-04-23 12:28                         ` Sagi Grimberg
     [not found]                         ` <a3264968-2d9e-bda5-1f23-74da248cf4d5-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
2017-04-23 13:35                           ` Max Gurtovoy
2017-04-23 13:35                             ` Max Gurtovoy
     [not found]                             ` <9a9668fa-87a7-e730-27e2-8a2b3e7fbc36-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-04-23 14:35                               ` Sagi Grimberg
2017-04-23 14:35                                 ` Sagi Grimberg
     [not found]                                 ` <8ed506ba-ae7b-af27-2d2a-9a434c22353c-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
2017-05-01 18:50                                   ` Doug Ledford
2017-05-01 18:50                                     ` Doug Ledford
     [not found]                                     ` <1493664645.3041.184.camel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-05-02 16:14                                       ` Max Gurtovoy
2017-05-02 16:14                                         ` Max Gurtovoy
     [not found]                                         ` <4a1c94b5-fe13-8b34-762f-e7465182ed27-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-05-02 16:39                                           ` Laurence Oberman
2017-05-02 16:39                                             ` Laurence Oberman

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