Re: [PATCH 09/13] sata_mv ncq Use DMA memory pools for hardware memory tables

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Mark Lord writes:
 > Tejun Heo wrote:
 > >..
 > > I'm skeptical about the benefit of IRQ coalescing on storage
 > > controllers.  Coalescing improves performance when there are many small
 > > requests to complete and if you put a lot of small non-consecutive
 > > requests to a disk, it gets really really really slow and IRQ coalescing
 > > just doesn't matter at all.  The only way to achieve high number of
 > > completions is to issue small commands to consecutive addresses which is
 > > just silly.  In storage, high volume transfer is achieved through
 > > request coalescing not completion coalescing and this is true for even SDDs.
 > ..
 > 
 > One cool thing with the Marvell cores, is that they actually implement
 > "transaction based" IRQ coalescing, whereby a number of related I/O commands
 > (say, all the RAID5 member commands generated by a single R/W request)
 > can be tagged together, generating an interrupt only when they all complete
 > (or after a timeout if something goes wrong).
 > 
 > We don't have anything resembling an appropriate abstraction for that yet,
 > so I doubt that we could really take advantage of it.

Promise SATA controllers have this feature too,
though sata_promise doesn't make use of it.
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