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From: Jeff Garzik <jeff@garzik.org>
To: Dan Williams <dan.j.williams@gmail.com>
Cc: NeilBrown <neilb@suse.de>,
	linux-raid@vger.kernel.org, akpm@osdl.org,
	linux-kernel@vger.kernel.org, christopher.leech@intel.com
Subject: Re: [PATCH 00/19] Hardware Accelerated MD RAID5: Introduction
Date: Wed, 13 Sep 2006 00:05:36 -0400	[thread overview]
Message-ID: <45078390.7010901@garzik.org> (raw)
In-Reply-To: <e9c3a7c20609112247u30685133kc84f094ce7854776@mail.gmail.com>

Dan Williams wrote:
> On 9/11/06, Jeff Garzik <jeff@garzik.org> wrote:
>> Dan Williams wrote:
>> > This is a frequently asked question, Alan Cox had the same one at OLS.
>> > The answer is "probably."  The only complication I currently see is
>> > where/how the stripe cache is maintained.  With the IOPs its easy
>> > because the DMA engines operate directly on kernel memory.  With the
>> > Promise card I believe they have memory on the card and it's not clear
>> > to me if the XOR engines on the card can deal with host memory.  Also,
>> > MD would need to be modified to handle a stripe cache located on a
>> > device, or somehow synchronize its local cache with card in a manner
>> > that is still able to beat software only MD.
>>
>> sata_sx4 operates through [standard PC] memory on the card, and you use
>> a DMA engine to copy memory to/from the card.
>>
>> [select chipsets supported by] sata_promise operates directly on host
>> memory.
>>
>> So, while sata_sx4 is farther away from your direct-host-memory model,
>> it also has much more potential for RAID acceleration:  ideally, RAID1
>> just copies data to the card once, then copies the data to multiple
>> drives from there.  Similarly with RAID5, you can eliminate copies and
>> offload XOR, presuming the drives are all connected to the same card.
> In the sata_promise case its straight forward, all that is needed is
> dmaengine drivers for the xor and memcpy engines.  This would be
> similar to the current I/OAT model where dma resources are provided by
> a PCI function.  The sata_sx4 case would need a different flavor of
> the dma_do_raid5_block_ops routine, one that understands where the
> cache is located.  MD would also need the capability to bypass the
> block layer since the data will have already been transferred to the
> card by a stripe cache operation
> 
> The RAID1 case give me pause because it seems any work along these
> lines requires that the implementation work for both MD and DM, which
> then eventually leads to being tasked with merging the two.

RAID5 has similar properties.  If all devices in a RAID5 array are 
attached to a single SX4 card, then a high level write to the RAID5 
array is passed directly to the card, which then performs XOR, striping, 
etc.

	Jeff




  reply	other threads:[~2006-09-13  4:05 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-09-11 23:00 Dan Williams
2006-09-11 23:17 ` [PATCH 01/19] raid5: raid5_do_soft_block_ops Dan Williams
2006-09-11 23:34   ` Jeff Garzik
2006-09-11 23:17 ` [PATCH 02/19] raid5: move write operations to a workqueue Dan Williams
2006-09-11 23:36   ` Jeff Garzik
2006-09-11 23:17 ` [PATCH 03/19] raid5: move check parity " Dan Williams
2006-09-11 23:17 ` [PATCH 04/19] raid5: move compute block " Dan Williams
2006-09-11 23:18 ` [PATCH 05/19] raid5: move read completion copies " Dan Williams
2006-09-11 23:18 ` [PATCH 06/19] raid5: move the reconstruct write expansion operation " Dan Williams
2006-09-11 23:18 ` [PATCH 07/19] raid5: remove compute_block and compute_parity5 Dan Williams
2006-09-11 23:18 ` [PATCH 08/19] dmaengine: enable multiple clients and operations Dan Williams
2006-09-11 23:44   ` Jeff Garzik
2006-09-12  0:14     ` Dan Williams
2006-09-12  0:52       ` Roland Dreier
2006-09-12  6:18         ` Dan Williams
2006-09-12  9:15           ` Evgeniy Polyakov
2006-09-13  4:04           ` Jeff Garzik
2006-09-15 16:38     ` Olof Johansson
2006-09-15 19:44       ` [PATCH] dmaengine: clean up and abstract function types (was Re: [PATCH 08/19] dmaengine: enable multiple clients and operations) Olof Johansson
2006-09-15 20:02         ` [PATCH] [v2] " Olof Johansson
2006-09-18 22:56         ` [PATCH] " Dan Williams
2006-09-19  1:05           ` Olof Johansson
2006-09-19 11:20             ` Alan Cox
2006-09-19 16:32               ` Olof Johansson
2006-09-11 23:18 ` [PATCH 09/19] dmaengine: reduce backend address permutations Dan Williams
2006-09-15 14:46   ` Olof Johansson
2006-09-11 23:18 ` [PATCH 10/19] dmaengine: expose per channel dma mapping characteristics to clients Dan Williams
2006-09-11 23:18 ` [PATCH 11/19] dmaengine: add memset as an asynchronous dma operation Dan Williams
2006-09-11 23:50   ` Jeff Garzik
2006-09-11 23:18 ` [PATCH 12/19] dmaengine: dma_async_memcpy_err for DMA engines that do not support memcpy Dan Williams
2006-09-11 23:51   ` Jeff Garzik
2006-09-11 23:18 ` [PATCH 13/19] dmaengine: add support for dma xor zero sum operations Dan Williams
2006-09-11 23:18 ` [PATCH 14/19] dmaengine: add dma_sync_wait Dan Williams
2006-09-11 23:52   ` Jeff Garzik
2006-09-11 23:18 ` [PATCH 15/19] dmaengine: raid5 dma client Dan Williams
2006-09-11 23:54   ` Jeff Garzik
2006-09-11 23:19 ` [PATCH 16/19] dmaengine: Driver for the Intel IOP 32x, 33x, and 13xx RAID engines Dan Williams
2006-09-15 14:57   ` Olof Johansson
2006-09-11 23:19 ` [PATCH 17/19] iop3xx: define IOP3XX_REG_ADDR[32|16|8] and clean up DMA/AAU defs Dan Williams
2006-09-11 23:55   ` Jeff Garzik
2006-09-11 23:19 ` [PATCH 18/19] iop3xx: Give Linux control over PCI (ATU) initialization Dan Williams
2006-09-11 23:56   ` Jeff Garzik
2006-09-11 23:19 ` [PATCH 19/19] iop3xx: IOP 32x and 33x support for the iop-adma driver Dan Williams
2006-09-11 23:38 ` [PATCH 00/19] Hardware Accelerated MD RAID5: Introduction Jeff Garzik
2006-09-11 23:53   ` Dan Williams
2006-09-12  2:41     ` Jeff Garzik
2006-09-12  5:47       ` Dan Williams
2006-09-13  4:05         ` Jeff Garzik [this message]
2006-09-13  7:15 ` Jakob Oestergaard
2006-09-13 19:17   ` Dan Williams
2006-09-14  7:42     ` Jakob Oestergaard
2006-10-11  1:46       ` Dan Williams
2006-10-08 22:18 ` Neil Brown
2006-10-10 18:23   ` Dan Williams
2006-10-11  2:44     ` Neil Brown

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