Re: [patch] Revert "block: remove artifical max_hw_sectors cap"

[Christoph Hellwig <hch@infradead.org>]

On Mon, Aug 10, 2015 at 01:23:48PM -0400, Jeff Moyer wrote:
> Unfortunately, I'm unable to reproduce your results (though my test
> setup uses SAS disks, not SATA).  I tried with a 10 data disk md RAID5,
> with 32k and 128k chunk sizes.  I modified the fio program to read/write
> multiples of the stripe width, and I also used aio-stress over a range
> of queue depth and I/O sizes for read, write, random read and random
> write.  I didn't see any measurable performance difference.  Do you
> still have access to your test setup?

Unfortuntately I don't have access to a large RAID setup at the moment.

> What do you think about reinstituting the artificial max_sectors_kb cap,
> but bumping the default up from 512KB to 1280KB?  I had our performance
> team run numbers on their test setup (which is a 12 disk raid0 with 32k
> chunk size, fwiw) with max_sectors_kb set to 1280 and, aside from one
> odd data point, things looked good.

Let's settle on that for 4.2 and then look it in more detail.

> 
> Cheers,
> Jeff
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